PRACTICAL   GEOLOGY 

AND 

MINERALOGY 


A  Short  Course  in  Mining  Science,  Designed  for  the  Student, 

Miner,  Prospector  and  General  Mining  Man.     Written 

From  the  Standpoint  of  a  Practical  Field  Man. 


REVISED  EDITION 


BY 

W.  D.  HAMMAN,  B.  Sc. 


THE  WAY  PRESS 

SOUTH  PASADENA,  CAL.,  U.  S.  A. 

1915 


Copyright   1915,  by 
W.  D.  HAMMAN 


PREFACE   TO   SECOND    EDITION 


The  intrusion  of  "Practical  Geology  and  Miner- 
alogy" into  the  domain  of  Mining  Science  was  at- 
tended with  serious  misgivings  on  the  part  of  the 
author.  A  fair  warning  had  been  given  by  those 
competent  to  advise  that  technical  subjects  could 
only  be  successfully  treated  in  technical  language; 
that  any  departure  from  recognized  standards 
would  prove  futile  if  not  an  absolute  failure. 

With  the  prospector's  instinct  for  new  fields 
and  with  a  firm  belief  that  a  common  school  educa- 
tion qualifies  any  one  to  understand  basic  principles 
of  any  science,  when  presented  in  common  every- 
day language,  the  well  meant  friendly  advice  had 
to  go  into  the  discard. 

The  occasion  for  a  second  edition  should  be 
conclusive  evidence  that  the  author's  estimate  of 
the  ability  of  the  average  person  was  not  wholly 
incorrect,  as  no  work  lacking  in  substantial  merit 
can  well  have  a  renewed  lease  of  life. 

The  kindly  criticism  of  this  work  by  scientists 
who  have  found  it  worthy  of  review,  is  appreciated 
and  has  enabled  a  correction  of  some  errors  of 
principle  and  expression  in  the  first  edition.  How- 
ever a  greater  source  of  satisfaction  has  been  af- 
forded by  kind  words  of  approval  from  students  in 
the  "School  of  Experience";  That  the  practical 


4  PREFACE  TO  SECOND  EDITION 

miner  and  prospector  in  the  field  have  been  able  to 
understand  and  profit  by  the  elementary  lessons  in 
mining  science,  is  nothing  short  of  an  inspiration. 

The  various  subjects  treated  in  this  work  would 
make  several  volumes  if  given  full  consideration. 
The  author's  aim  has  been  simply  to  open  up  each 
subject — state  fundamental  principles  and  facts  in 
an  interesting  way,  hoping  to  stimulate  a  desire  on 
the  part  of  the  reader  for  more  knowledge. 

Students  and  perhaps  graduates  of  mining 
schools  often  forget  elementary  principles,  so  that  a 
brief  review  such  as  is  herein  given  often  proves  of 
much  value  in  removing  mental  cobwebs. 

As  a  text  book  for  study  at  home  as  well  as  in 
schools  giving  a  brief  course  in  mining,  many  have 
found  this  little  book  of  great  service,  and  the  hope 
is  cherished  that  this  field  of  usefulness  will  be 
greatly  enlarged. 

Conscious  that  all  human  effort  is  imperfect,  the 
author  will  welcome  constructive  criticism  from 
any  source. 

W.   D.   H. 
August,  1915. 


TABLE   OF   CONTENTS 


FOREWORD 

1 — Mental  and  Moral  Knowledge. — What  is  Sci- 
ence?— What  We  Do  Not  Know. — What  Are  Natural 
Laws? 

Part  I  GEOLOGY 

What  is  Geology? — Why  a  Knowledge  of  Geology 
is  Necessary. — What  is  the  Earth? — What  is  the  Earth's 
Structure? — What  Materials  Make  Up  the  Earth? — Is 
the  Earth's  Interior  Hot? — Conclusion  from  Evidence. — 
What  are  Nebulae  and  Meteors? — What  are  the  Nebular 
and  Meteoritic  Theories? — What  Practical  Use  are 
These  Theories? — What  are  the  Three  Kingdoms? — Is 
the  Earth's  Crust  Stable? — What  Proofs  are  there  of 
Earth  Movements  Today? — What  Proofs  Exist  That 
Mountains  Have  Been  Uplifted? — What  Relation  do 
Mountains  Sustain  to  Mineral  Deposits? — What  Crust 
Changes  are  Due  to  Action  of  Air  and  Water? — What 
Other  Forces  Assist  Air  and  Water? — What  are  Gla- 
ciers?— What  Changes  do  They  Produce? — What  Evi- 
dence is  There  of  Glacial  Action  on  the  Earth's  Crust? 
What  Was  the  Cause  of 'This  Glacial  Drift?— Was  the 
Pacific  Coast  Affected  by  Glaciers? — What  are  Known 
as  the  Geologic  Ages? — How  do  Fossils  Record  Earth's 
History? — How  is  the  History  of  the  Earth's  Crust 
Divided?  —  What  Constitutes  the  Azoic  Era?  —  What 


TABLE  OF  CONTENTS 


Marks  the  Paleozoic  Era? — What  Distinguishes  the  Silu- 
rian Age? — How  Can  We  Tell  the  Devonian  Rocks? — 
What  is  Known  of  the  Carboniferous  Age? — What 
Characterizes  the  Mesozoic  Era? — What  Peculiarity  has 
the  Cretaceous  Period? — What  is  the  Cenozoic  Age? — 
Tertiary  Period. — What  Changes  Occurred  in  the  Quar- 
ternary  Period? — What  Practical  Mining  Lessons  do  the 
Geologic  Ages  Teach  Us? — What  are  the  Three  Zones  in 
the  Earth's  Crust? — What  Characterizes  the  Oxide  or 
Fracture  Zone? — What  Distinguishes  the  Sulphide  or 
Fracture  and  Flowage  Zone? — What  do  We  Know 
About  the  Molten  or  Flowage  Zone? — How  to  Use 
Geological  Survey  Maps  and  Reports. 

Part  II  PETROLOGY 

What  is  Rock? — What  is  Petrology? — Of  What  are 
Rocks  Composed? — What  are  Calcereous  Rocks? — What 
is  the  Origin  of  Calcareous  Rock? — How  do  Limestone 
and  Dolomite  Differ? — What  is  the  Composition  of 
Marble? — What  is  Gypsum? — What  are  Silicious 
Stones? — What  is  the  Origin  of  Quartz? — How  are 
Rocks  Classified? — What  are  Aqueous  Rocks? — What 
are  Igneous  Rocks? — What  are  Trap  Rocks? — What  are 
the  Volcanic  Rocks? — What  are  the  Metamorphic  Rocks? 
— Granite,  What  It  is  and  How  Formed? — How  do 
Rocks  Differ  in  Structure  ?< — What  are  Strata,  Forma- 
tions and  Groups? — What  are  Folds? — What  are  Faults? 
—What  are  the  Unstratified  Rocks? — What  are  Dikes 
and  Veins? — What  is  the  Origin  of  Veins  and  Dikes? 

Part  III  MINERALOGY 

Introduction — What  is  a  Mineral? — How  are  Min- 
erals Formed? — What  is  Mineralogy? — What  are  Ele- 
ments?— What  are  Compounds? — What  are  Symbols  and 


TABLE  OF  CONTENTS 


Formulas? — How  are  Elements  Classified? — How  are 
Minerals  Grouped ? — What  do  the  Endings  Signify? — 
Oxide — Sulphides —  Arsenides —  Antimonides — Tellurides 
— Chlorides — Iodides —  Bromides —  Fluorides —  Carbon- 
ates— Silicates  —  Nitrates  —  Borates  —  Phosphates — Tung- 
states  —  Molybdates  —  Vanadates  —  What  are  Known  as 
Alkali  Minerals? — What  are  the  Acid  Minerals? 

PHYSICAL  PROPERTIES  OF  MINERALS 

(1)  Luster— (2)  Color— (3)  Hardness —Table  of 
Hardness  of  Common  Minerals — (4)  Specific  Gravity — 
(5)  Fracture— (6)  Cleavage— (7)  Tenacity—  (8)  Crys- 
talline Structure  —  Crystal  Form  —  Crystallography  — 
What  Causes  the  Endless  Variety  of  Crystals? — What 
are  Pseudomorphs  ? — Internal  Imperfections  and  Inclus- 
ions— Other  Simple  Mineral  Tests — Table  of  Fusibility 
of  Common  Minerals — Acid  Mineral  Tests. 
CHEMICAL  PROPERTIES  OF  MINERALS 

How  to  Examine  and  Determine  Minerals. 
DESCRIPTIVE  MINERALOGY 

Gold  (Au)  Minerals — Silver  (Ag)  Minerals — Cop- 
per (Cu)  Minerals— Lead  (Pb)  Minerals— Zinc  (Zn) 
Minerals — Cobalt  (Co)  Minerals — Nickel  (Ni)  Miner- 
als— Mercury  (Hg)  Minerals — Tin  (Sn)  Minerals 
Tungsten  (W)  Minerals — Titanium  (Ti)  Minerals — 
Vanadium  (V)  Minerals — Uranium  (U)  Minerals — 
Molybdenum  (Mo)  Minerals — Bismuth  (Bi)  Minerals — 
Platinum  (Pt)  Minerals — Iron  (Fe)  Minerals — Manga- 
nese (Mn)  Minerals — Aluminum  (Al)  Minerals — Cal- 
cium (Ca)  Minerals — Barium  (Ba)  Minerals — Sodium 
(Na)  Minerals — Potassium  (K)  Minerals — Magnesium 
(Mg)  Minerals— Carbon  (C)  Minerals— Silica  (Si) 


8 TABLE  OF  CONTENTS 

Minerals — What   are   the   Gangue      Minerals? — How     to 
Make  Practical  Application  of  Physical  Properties. 

Part  IV  MINERAL  DEPOSITS 

What  are  the  Relative  Proportions  of  the  Elements? 
— What  is  the  Origin  of  Minerals? — What  is  the  Sea 
Water  Theory? — What  is  the  Igneous  or  Subterranean 
Theory? — Conclusions  From  the  Evidence. — How  are 
Mineral  Deposits  Formed? — What  are  the  Concentrating 
Agencies  ? 

POPULAR  THEORIES  AS  TO  GENESIS  OF  ORE  DEPOSITS 

(1)  What  is  the  Theory  of  Contemporaneous  For- 
mation?— (2)  What  is  the  Theory  of  Igneous  Injection? 
—(3)  What  is  the  Electric  Current  Theory?— (4)  What 
is  the  Theory  of  Descending  Waters? — (5)  What  is  the 
Sublimation  Theory? — (6)  What  is  the  Theory  of  Lat- 
eral Secretion? — (7)  What  is  the  Theory  of  Ascending 
Waters? — (8)  Theory  of  Replacement. — What  Conclus- 
ions May  Be  Drawn  From  These  Theories? — Ideal  Sec- 
tion Illustrating  Origin  of  Ore  Deposits. — What  is  Na- 
ture's Preparation  for  Mineral  Deposits? 

CLASSIFICATION  OF  MINERAL  DEPOSITS 

Beds  or  Stratified  Deposits — What  are  They? — How 
are  Bedded  Deposits  Formed? — What  are  Placer  and 
Beach  Deposits? — What  is  the  Origin  of  Ancient  River 
Deposits? — How  are  Beach  Placers  Formed? — What  is 
the  Origin  of  Nuggets  in  Placers? — Coal  Measures — 
What  are  They  and  How  Formed? — Petroleum — What 
is  It  and  How  Formed? — Unstratified  Deposits. — What 
Constitutes  an  Ore? — What  Physical  Conditions  Influ- 
ence Ore  Deposits? — Veins — What  are  They? — What 
are  Ore  Shoots — Do  Veins  Grow  Richer  With  Depth  ? 


TABLE  OF  CONTENTS 


How  VEINS  ARE  CLASSIFIED 

Fissure  Veins — What  are  They? — How  May  the 
Age  of  Fissure  Veins  Be  Determined? — Contact  Veins — 
What  are  They?— Gash  Veins— What  are  They?— What 
are  Segregation  Veins? 

IRREGULAR  ORE  DEPOSITS 

What  are  Chamber  Deposits? — What  are  Impregna- 
tion and  Stockwork  Deposits? — What  are  Fahlbands? — 
What  are  the  Common  Errors  in  Regard  to  Ore  Deposits? 
— General  Principles  Governing  Ore  Deposits — How  Do 
Faults  Affect  Ore  Bodies? — Concluding  Observations. 


AUTHOR'S  PREFACE 


There  are  perhaps  more  people  interested  in  mining  who 
know  nothing  of  the  underlying  principles  than  in  any  other 
industry.  This  is  largely  due  to  the  widespread  belief  that  it 
is  all  a  matter  of  chance  or  luck,  whether  success  or  failure 
results.  Years  of  practical  experience  in  the  different  branches 
of  the  mining  business  have  convinced  the  author  that  nearly 
all  failures  in  mining  are  due  to  ignorance  of  the  elementary 
principles  of  mining  science.  This  is  no  reflection  on  those 
engaged  in  mining  as  no  other  industry  contains  a  larger 
proportion  of  intelligent,  wide-awake  people,  but  this  condi- 
tion is  due  almost  wholly  to  the  absence  of  practical,  non- 
technical books  on  mining  subjects.  Realizing  this  serious 
handicap  to  the  mining  business,  the  author  has  endeavored 
to  rise  to  the  occasion,  and  supply  this  "long-felt  want." 

Science  is  a  dry  subject  to  many,  especially  if  presented  in 
academic  style  and  technical  language.  While  it  is  impossi- 
ble to  treat  science  in  story-book  fashion,  yet  the  author  be- 
lieves it  is  possible  to  popularize  mining  science,  by  "cutting 
out"  unimportant  matter  and  confining  the  scope  to  simple, 
practical  every-day  phases  of  the  mining  business. 

There  is  a  fascination  about  mining,  and  the  author's 
central  idea  has  been  to  present  his  several  subjects  in  such  a 
way  as  to  arouse  interest  and  encourage  the  further  study  of 
mining  science.  Illustrations  have  been  freely  used  to  break 


12  AUTHOR'S  PREFACE 

the  monotony  and  to  firmly  fix  the  principles  in  the  mind  of 
the  reader,  by  means  of  these  object  lessons. 

Nearly  every  subject  is  introduced  by  a  pertinent  question 
and  the  paragraph  following  is  devoted  to  answering  the 
query  raised,  so  that  a  live  practical  issue  is  raised  on  every 
page. 

Centuries  ago  the  wisest  man  that  ever  lived  said,  "There 
is  nothing  new  under  the  sun."  The  same  old  sun  shines 
today  and  beholds  nothing  new;  elements  and  principles  will 
ever  remain  the  same  throughout  all  time. 

Mining  is  an  old  industry  and  much  has  been  said  and 
written  concerning  it.  But  mining  wisdom,  like  the  precious 
element — gold — though  everywhere  present,  yet  requires  to 
be  collected,  concentrated  and  refined  to  be  of  use  to  man. 
This  has  been  the  task  at  hand  in  the  preparation  of  this  work 
and  it  is  for  the  reader  to  judge  the  merits  of  the  processes 
used. 

The  author  has  discovered  no  new  facts  or  principles,  but 
has  not  hesitated  to  appropriate  anything  of  practical  value 
within  range  and  no  acknowledgment  can  well  be  made  as  to 
any  particular  source. 

A  list  of  the  authorities  consulted  in  the  preparation  of  this 
work  would  read  too  much  like  a  catalogue  of  the  leading 
books  on  mining  science,  and  would  serve  no  useful  purpose. 
Whatever  merit  this  volume  contains  is  due  to  sampling, 
grading  and  concentrating  the  rough  material  at  hand,  care- 
fully selecting  the  rich  "Pay-streak"  and  consigning  the  "low- 
grade"  to  the  "waste  dump." 

Care  has  been  taken,  however,  to  be  accurate,  and  nothing 
herein  contained  lacks  support  of  authority.  Despite  constant 


AUTHOR'S  PREFACE  13 

watchfulness,    however,    errors    will    creep    in    so    that    the 
author's  meaning  is  sometimes  changed. 

The  technical  reader  may  find  cause  to  criticise  the 
elementary  character  of  this  work,  but  it  was  not  designed 
for  his  benefit;  although  he  may  find  profit  in  a  few  lessons 
learned  in  the  School  of  Experience. 

The  author  has  constantly  kept  in  view  the  needs  of  the 
great  mass  of  mining  men,  who  have  not  had  the  advantage  of 
a  course  in  a  Mining  School.  While  the  limits  of  such  a  work 
will  not  permit  more  than  brief  outline  of  the  subjects 
treated,  yet  such  important  subjects  as  "Ore  Deposits,"  are 
discussed  so  fully  that  even  the  mining  expert  may  possibly 
derive  something  of  benefit  therefrom. 

Should  this  work  find  favor  with  that  noble  band  of 
mining  men  who  are  seeking  to  extract  pure  "untainted" 
wealth  from  Nature's  Vast  Treasure-house,  and  also  assist 
in  raising  the  standard  of  the  mining  industry  to  that  exalted 
position  to  which  it  is  justly  entitled,  the  author  shall  feel 
amply  repaid  for  his  humble  efforts. 

Faithfully  yours, 

W.  D.  HAMMAN. 
Los  Angeles,  California,  August,  1911. 


PRACTICAL  GEOLOGY  AND 
MINERALOGY 

Foreword 

We  are  endowed  by  an  All  Wise  Providence  with  five 
senses:  touch,  taste,  smell,  sight  and  hearing.  The  nerves 
from  these  organs  run  to  headquarters — the  brain,  and  the 
sensations  are  impressed  into  our  consciousness  and  as  a 
result  We  Know. 

For  example:  We  touch  a  hot  iron.  A  message  is 
flashed  along  the  nerve-wires  and  recorded  in  the  brain. 
Instantly  an  order  is  dispatched  to  remove  the  member.  The 
whole  process  is  complete  in  the  twinkling  of  an  eye.  The 
other  four  senses  act  in  a  similar  way,  and  as  a  result  of  this 
physical  evidence  a  normal  mind  Knows.  An  idiot,  however, 
with  all  the  senses  named,  cannot  know  because  he  has  no 
mind  to  receive  and  use  the  evidence  of  the  senses.  There 
is  also  a  vast  difference  in  the  minds  of  intelligent  persons. 
One  may  look  at  a  rock  and  see  nothing  of  interest,  and  cast 
it  aside.  Another  person,  trained  in  Geology  and  Mineral- 
ogy, sees  evidence  of  great  riches,  material  for  a  lecture 
discourse  or  the  reflection  of  God's  infinite  wisdom  and 
power.  What  makes  the  difference?  It  is  partly  in  the 
quality  of  the  brain  itself,  but  more  largely  a  matter  of 


16      PRACTICAL  GEOLOGY  AND  MINERALOGY 

mental  training.  The  man  who  says  he  will  believe  nothing 
that  he  cannot  see,  touch,  taste,  hear  or  smell,  will  hardly 
reach  the  first  mile-post  on  the  road  to  knowledge. 

Mental  and  Moral  Knowledge 

There  is  another  sort  of  knowledge,  equally  important, 
in  which  the  physical  senses  are  seldom  called  into  play. 
The  evidence  is  often  circumstantial,  or  the  result  of  expert 
knowledge,  or  unusual  skill  in  a  certain  line.  And  since 
facts  are  proven  in  our  courts  by  such  testimony,  we  also 
should  not  hesitate  to  use  it. 

For  example:  The  scientific  men  of  his  day  knew  the 
earth  was  round,  long  before  Columbus  set  out  on  his  voy- 
age of  discovery.  How  did  they  know  it?  By  expert 
knowledge  acquired  by  long  study  of  the  Solar  System, 
such  evidence  as  appealed  to  their  reason,  but  even  in  this 
day,  when  hundreds  of  ships  yearly  sail  around  it,  some 
still  believe  the  world  flat,  because  it  appears  so  to  their 
narrow  vision.  Astronomers  measure  the  distance  to  the 
sun  and  calculate  the  movements  of  the  heavenly  bodies  so 
accurately  that  the  exact  minute  of  an  eclipse  or  the  crossing 
of  the  earth's  path  by  a  comet,  is  predicted  long  in  advance. 
We  also  might  do  this  with  as  much  study,  but  the  field  of 
knowledge  is  too  broad  and  the  human  mind  too  limited  for 
any  person  to  learn  it  all,  and  for  that  reason  mankind  in 
general  is  forced  to  accept  a  great  many  things  on  expert 
testimony,  which  we  call  Authority. 

What  is  Science? 

All  knowledge,  however  gained,  that  has  been  proven 
by  exact  observation  and  correct  reasoning,  is  called  Science. 
In  other  words,  only  truths,  facts  that  have  been  collected 
and  classified,  may  properly  be  called  Science.  Any  collection 


FOREWORD  1 7 


of  untruths,  no  matter  how  cleverly  arranged  and  presented, 
would  be  unworthy  of  the  name  Science,  because  unsupported 
by  proper  evidence.  An  actual  demonstration  is  not  always 
necessary  ,  but  there  must  be  such  probable  or  moral  evidence, 
on  which  to  base  a  belief  or  judgment  or  the  name  science 
may  not  properly  be  given  it. 

What  We  Do  Not  Know. 

In  all  sciences  there  are  many  mysterious  things  which 
we  may  only  know  in  part  and  can  not  fully  explain,  much 
less  actually  prove.  In  the  study  of  such  subjects,  a  few 
known  things  that  fit  fairly  well  into  each  other  are  often 
used  to  construct  a  theory  or  hypothesis  and  with  this  as  a 
basis  of  reasoning,  we  are  often  able  to  solve  a  problem  that 
is  otherwise  impossible. 

To  illustrate:  Electricity  is  almost  a  household  necessity 
today.  But  we  do  not  even  know  what  electricity  is,  and  no 
one  has  yet  been  able  to  analyze  or  define  it.  Yet  we  do 
know  how  it  acts  and  man  has  been  able  to  harness  it  and  in  a 
measure  control  it,  but  still  electricity  remains  a  mysterious 
force.  Science  has  been  unable  to  fully  explain  the  origin, 
or  fix  the  actual  age  of  the  earth  upon  which  we  live,  but 
that  does  not  prevent  our  laying  hold  of  those  truths  and 
facts  that  science  has  extracted  from  the  Book  of  Nature  as 
written  in  the  rocks  of  the  earth. 

What  Are  Natural  Laws? 

In  nature  nothing  ever  "just  happens"  or  comes  by 
"chance."  Every  where  there  is  order  and  system.  Every 
creature  must  have  had  a  Creator.  Every  design  calls  for  a 
designer  and  every  law  pre-supposes  a  law-giver. 

Law  has  been  well  defined  to  be  "a  rule  of  action,"  so  a 
natural  law  is  nature's  rule  of  action.  Nature's  laws  have 


18       PRACTICAL  GEOLOGY  AND  MINERALOGY 

always  existed,  but  man  has  been  slow  to  discover  and 
classify  them.  For  illustration,  as  Newton  lay  under  a  tree, 
an  apple  fell  and  struck  him  in  the  face.  This  set  him  to 
thinking.  "Why  did  not  the  apple  fall  up  instead  of  down?" 
and  the  result  of  this  thinking  led  to  the  discovery  of  the  Law 
of  Gravitation,  that  all  bodies  left  unsupported  fall,  in  a  dir- 
ect line  toward  the  center  of  the  earth.  This,  like  all  other 
natural  laws,  is  unchangeable;  the  same  for  all  times  and 
places.  In  the  study  of  mining  science  these  fundamental 
principles  must  ever  be  borne  in  mind:  "That  like  causes 
produce  like  effects"  and  "similar  effects  may  always  be 
traced  to  similar  causes";  we  must  reason  from  known  facts 
or  conditions  back  to  the  unknown.  These  principles  underly 
all  science. 

To  illustrate:  If  the  world  was  originally  a  body  of  gas, 
as  many  scientists  believe,  it  condensed  just  as  similar  bodies 
condense  today.  If  it  was  ever  a  molten  mass,  it  cooled  and 
became  a  solid  just  as  a  molten  globe  would  now  cool  and 
solidify.  Likewise,  just  as  elements  unite  to  form  compounds 
in  the  chemist's  laboratory  today,  so  in  nature's  great  labor- 
atory the  wonderful  variety  of  mineral  compounds  have  been 
formed  in  obedience  to  the  same  unchanging  natural  laws. 


PART  1 

GEOLOGY 


PARTI 

GEOLOGY 

What  is  Geology? 

1.  The  word  Geology  is  from  geo   (Earth)   and  logos 
(Study)  and  literally  means  Earth  study.     It  is  the  Science 
that  teaches  the  Earth's  history,  as  written  in  the  rocks.    To 
be  able  to  read  and  understand  Nature's  language,  requires 
a  knowledge  of  Nature's  Alphabet,  which  is  to  be  found  in 
the  Science  of  Geology. 

As  a  Science,  Geology  is  very  broad  and  its  proper  study 
requires  some  knowledge  of  all  the  natural  Sciences,  most 
particularly  Physics  and  Chemistry,  which  subjects  are 
outside  the  scope  of  this  work. 

Why  a  Knowledge  of  Geology  is  Necessary 

2.  The  purposes  of  the  study  of  Geology  may  be  classed 
under  three  heads:     (a)   To  enable  us  to  discover  the  prin- 
ciples and  forces  that  brought  the  Earth  into  existence,that 
governed  its  development  and  must  control  its  final  destiny; 
(b)   To  aid  us  in  tracing  the  earth's  history  as  recorded  in 
the  rocky  Book  of  Nature,  in  which  ' 'every  trace  becomes  a 
letter,  every  fragment  a  word,  and  every  animal  or  vegetable 
fossil   forms  a  chapter";    (c)   Lastly  and  above  all   is  the 
practical  benefit  to  be  derived  from  a  knowledge  of  Geology 
to  the  mining  man.    Within  the  rock-ribbed  earth's  crust  lies 


22      PRACTICAL  GEOLOGY  AND  MINERALOGY 

the  mineral  wealth  he  seeks.  A  knowledge  of  the  earth,  its 
structure,  and  changes  as  well  as  the  principles  governing  the 
formation  of  minerals  and  ore  deposits,  is  absolutely  necessary 
to  success  in  exploring,  developing  and  extracting  minerals 
and  metals  from  Nature's  vast  store-house. 

Nature  is  not  prodigal  in  distributing  her  precious  gems 
and  metals,  whose  value  so  largely  depends  upon  their  scarc- 
ity. The  richest  treasures  are  secreted  in  the  bosom  of 
Mother  Earth,  and  only  those  who  diligently  study  Nature's 
laws  and  labor  in  harmony  with  them  can  secure  the  reward 
due  to  well  directed  industry. 

What  is  the  Earth? 

3.  The  Earth  is  one  in  the  system  of  planets  that  revolve 
in  regular  orbits  with  the  sun  as  the  central  object.  It  is 
third  in  distance  from  the  sun  and  sixth  in  relative  size. 
The  Earth  is  a  great  magnet,  the  north  pole  of  which  always 
points  to  the  North  Star  (Polaris)  no  matter  what  position 
it  assumes  in  its  orbit. 

The  form  of  the  earth  is  that  of  a  globe  or  sphere.  It  is 
slightly  flattened  at  the  poles  due  to  rotation  on  its  axis. 
Its  diameter  is  about  8,000  miles  and  its  circumference  a  little 
over  three  times  that  amount.  Science  tells  us  there  is  no. 
such  a  thing  as  rest  in  nature;  and  the  earth  is  a  fitting 
example  of  this  unrest.  It  has  a  motion  on  its  own  axis  of 
more  than  1,000  miles  an  hour  and  in  its  orbit  around  the 
sun  has  a  speed  of  eighteen  miles  a  second,  or  seventy-five 
times  as  swift  as  a  cannon  ball.  In  addition  to  these  two 
motions  of  the  whole  Earth,  the  water  and  air  are  in  constant 
motion,  while  the  solid  portion  of  the  Earth  rises  here  and 
falls  there,  but  so  slowly  as  to  be  scarcely  perceptible  to  the 
ordinary  observer. 


GEOLOGY  23 


What  is  the  Earth's  Structure? 

4.  To  simplify  the  study  of  the  Earth,  the  Geologist 
divides  it  into  two  parts: 

( 1 )  Crust,  and 

(2)  Interior. 

The  interior  of  the  earth  has  not  been  penetrated  to 
exceed  a  few  miles,  beyond  which  we  know  nothing,  except 
from  the  evidence  of  holes  or  shafts  made  in  the  crust  by  man. 

The  Science  of  Geology  relates  only  to  the  known  portion 
called  the  crust.  Geography  divides  the  Earth's  surface  into 
land  and  water,  but  the  water  which  covers  three-fourths 
of  the  globe  is  not  considered  by  the  Geologist  as  any  part  of 
the  earth  no  more  than  the  atmosphere  that  surrounds  it,  so 
we  must  consider  air  and  water  apart  from  earth,  simply 
as  Envelopes  enclosing  the  Earth,  much  as  an  envelope  en- 
closes a  written  letter. 

The  highest  mountain  rises  over  five  miles  above  sea 
level,  and  the  greatest  known  depth  of  the  sea  is  about  eight 
miles,  which  would  make  the  lowest  point  in  the  sea  about 
thirteen  miles  nearer  the  Earth's  center  than  the  top  of  the 
highest  mountain. 

In  Fig.  1  is  shown  an  elevated  section  of  the  Earth's 
crust,  and  Fig.  2  is  a  section  of  the  crust  under  the  sea, 
which  serves  to  show  that  there  are  hills,  valleys  and 
mountains  under  the  water  similar  to  those  on  the  land. 
There  is  also  positive  evidence  that  what  is  now  the  Land 
was  covered  by  the  sea,  not-  only  once  but  many  times  in  the 
Earth's  history,  but  this  will  be  treated  in  a  separate  subject. 

What  Materials  Make  Up  the  Earth? 

5.  Science  has  analyzed  some  eighty  forms  of  matter 


GEOLOGY  25 

that  make  up   the  Earth's  crust,  called   Elements.     These 
elements  are  divided  into — 

(1)  Solids. 

(2)  Liquids. 

(3)  Gases. 

The  gaseous  portion  is  mainly  found  in  the  atmosphere, 
which  is  a  mixture  of  two  gases, — Oxygen  and  Nitrogen, 
together  with  small  quantities  of  carbon,  acids  and  alkalies. 
Water  is  a  liquid,  but  composed  of  two  gases,  Oxygen  and 
Hydrogen  and  small  quantities  of  minerals  in  solution. 
Solids — These  form  the  Earth's  crust  though  water  and  gases 
enter  into  the  composition  of  most  all  solids  to  some  extent. 
Nearly  all  the  metals  and  minerals  are  solids,  under  ordinary- 
conditions. 

These  three  forms  of  matter  may  be  changed  at  will  in 
the  chemist's  laboratory,  through  the  agency  of  heat.  A 
common  example  is  ice — a  solid.  Heat  causes  this  to  melt 
and  form  water, — a  liquid;  a  greater  degree  of  heat  changes 
the  water  into  steam, — a  gas.  By  taking  away  the  heat,  the 
steam  condenses  into  water  and  thence  into  ice  again.  There 
are  good  grounds  for  believing  that  originally  all  forms  of 
matter  were  in  a  gaseous  state ;  in  cooling,  certain  gases  united 
in  fixed  proportions,  forming  liquid — water,  the  other  gases 
condensed  and  separated  out  forming  solids, — rocks,  and  the 
remaining  gases  compose  the  atmosphere  today. 

The  forces  in  nature  act  and  react  on  the  various  elements, 
creating  endless  changes  and  combinations  that  often  puzzle 
the  scientist. 

What  is  Known  of  the  Earth's  Origin? 

6.     The  Mosaic  account  of  creation  is  not  fully  accepted 


26      PRACTICAL  GEOLOGY  AND  MINERALOGY 

by  Geologists,  but  any  seeming  conflict  is  doubtless  due  to  a 
misunderstanding  of  the  language  of  the  text.  The  "Six 
Days  of  Creation"  in  Genesis  are  now  regarded  by  those 
who  have  made  translation  a  study  to  mean,  not  six  literal 
days,  but  six  periods  of  time  of  thousands  or  even  millions  of 
years.  We  shall  see  later  that  the  Geologic  Ages  corespond 
very  closely  to  the  Bible  days,  or  periods.  Science  proves  the 
order  of  creation  began  with  the  lowest  and  advanced  to  the 
highest  form  of  animal  life  until  it  reached  the  climax  in  man, 
thus  confirming  the  Holy  Writ. 

"In  the  beginning,  God  created  the  heavens  and  the 
earth,"  declares  Moses.  Geologists  agree  that  the  earth  has 
not  always  existed,  at  least  not  in  its  present  form ;  although 
the  elements  composing  it,  being  indestructible,  must  always 
have  existed. 

We  have  then  two  courses  open  to  our  reason:  first, 
Accept  the  Mosaic  account  as  authority  on  the  subject;  and 
second,  take  such  known  facts,  as  are  shown  by  proper  evi- 
dence, and  forge  these  link  by  link  into  a  chain  of  reason, 
and  thus  endeavor  to  trace  back  to  the  "Great  first  Cause." 

Is  the  Earth's  Interior  Hot? 

7.  The  Earth's  crust  which  has  been  explored  by  man 
bears  about  the  same  relation  to  the  whole  globe  as  the  skin 
of  an  apple  bears  to  the  whole  apple:  A  slight  scratch  in  the 
varnish  of  a  school  globe  would  exaggerate  by  comparison — 
the  deepest  shafts  dug  by  man  in  the  real  globe. 

It  is  generally  believed  that  the  interior  of  the  Earth  is  in 
a  highly  heated  condition,  perhaps  in  a  molten  state.-  Mere 
belief  is  not  science,  so  it  is  necessary  to  examine  the  evidence 
to  support  such  a  belief. 


GEOLOGY  27 

8.  (a)   THE  TEMPERATURE  INCREASES  WITH  DEPTH. 
The     temperature     has     been     taken     at     different     depths 
in   the  world's   deepest   mines.     The   rate  of   heat   increase 
varies    somewhat    in    different    countries    and    sections,    but 
always   gets   warmer   from    the    surface    downward ;     the 
average    being    about    one    degree    for    each    sixty    feet    of 
depth.     On  this  basis  at  a  depth  of  twenty-five  miles  the 
principal  metals  and  rocks  would  melt,  and  at  fifty  miles 
depth  the  heat  would  be  sufficient  to  change  all  elements  to  the 
gaseous  state,  if  the  pressure  of  the  mass  above  did  not  pre- 
vent.    The  temperature  at  the  bottom  of  a  well  recently 
drilled  in   Pennsylvania,  6775   feet,  registered   145   degrees 
Fahrenheit. 

9.  (b)     WATER    FROM    ARTESIAN    WELLS  is   HOT. 
In    some   countries   Artesian     Wells     give     out     wrater    so 
hot  that  it  is  piped  through  buildings  to  heat  them  in  the 
place  of  fire  heat. 

10.  (c)     HOT      SPRINGS     AND      GEYSERS.       These 
are  found  in  many  parts  of  the  world  varying  somewhat  in 
temperature,   but  all   are  so  hot  as  to  point  to  a  common 
source  within  Earth.     The  Arkansas  Hot   Springs  have  a 
heat  of    180   degrees  while  the   Geysers  of   California  and 
Iceland  are  fountains  of  boiling  water  that  will  cook  an  egg 
in  a  few  minutes. 

11.  (d)     CRUST     ELEVATION     AND     DEPRESSION. 
The  mountains     bear     unmistakable     evidence     of     having 
been  uplifted  by  some  giant  force ;  in  other  places  what  were 
formerly  elevations  have  sunken  to  form  basins,  or  to  fill  the 
nnderground  cavities  formed  by  uplifts  elsewhere.     Many  of 
the  rocks  of  the  earth's  crust  have  been  fused  and  crystallized, 
which  could  have  been  done  by  no  other  agency  except  heat. 


28      PRACTICAL  GEOLOGY  AND  MINERALOGY 

12.  (e)     VOLCANOES.     In   many  parts  of   the  Earth 
today    there    are    volcanoes    throwing    up    hot    vapors    and 
molten  matter,  some  of  which  are  in  the  Polar  regions  of 
perpetual  snow  and  ice.    The  craters  of  extinct  volcanoes  are 
found  today  in  many  places,  some  a  mile  or  more  in  diameter, 
showing  that  in  former  ages  volcanoes  were  more  common 
and  of  greater  violence.     They  appear  to  be  smoke-stacks 
of  the  central  fiery  furnace  beneath.     Cities  now  lie  buried 
by  lava  and  ashes  of  volcanoes  in  past  ages. 

13.  (f)      EARTHQUAKES.     Hundreds     of     earthquake 
shocks   have   been    recorded    within    the    last     fifty     years. 
The  San  Francisco  earthquake  is  of  such  recent  occurrence 
as  to  be  familiar  to  all. 

Scientists  are  not  fully  agreed  as  to  the  causes,  some 
erroneously  attribute  earthquakes  to  tidal  waves  in  the 
ocean,  but  these  are  the  effect,  not  the  cause.  Geologists 
generally  believe  that  earthquakes  are  a  result  of  contraction 
in  the  earth's  crust  due  to  cooling.  All  are  agreed,  however, 
that  these  terrific  convulsions  are  due  to  the  heat  in  the 
interior  of  the  earth. 

Conclusion  From  Evidence 

14.  This   accumulated   evidence   proves  without   doubt 
that   the   earth's   interior   is  very   hot.     The  question   then 
arises,  "what  is  the  origin  of  this  heat?"     Scientists  are  not 
entirely  agreed  on  this  question.     We  know  that  the  sun  is 
the  great  source  of  heat  as  well  as  light,  but  the  sun  can 
only  warm  the  atmosphere  and  a  little  of  the  outside  crust. 
No    fuel   within   the   earth   could   long   burn    without    the 
oxygen  of  the  air. 

It  is  well  known  that  friction  produces  heat  and  primi- 
tive man  lighted  his  fires  by  rubbing  together  wood  or  stone 


GEOLOGY  29 

and  by  striking  fire  with  flint.  Pressure  also  generates  heat 
and  some  scientists  conclude  the  weight  of  the  crust  and  the 
continual  movement  of  the  mass  would  account  for  the  in- 
ternal heat,  but  it  hardly  seems  reasonable  to  trace  the  earth's 
heat  to  that  source  alone  and  this  forces  us  to  look  to  outside 
causes. 

What  are  Nebulae  and  Meteors? 

15.  Look  up  into  the  heavens  any  clear  night  and  behold 
a   bright   pathway,   called   the   Milky  Way.     Astronomers 
with  their  delicate  instruments  distinguish  luminous  matter 
about  the  stars,  which  by  its  color  in  the  spectrum   they 
pronounce  a  gas  similar  to  that  manufactured  in  the  labor- 
atory.     Comets,   those  outlaws   of   the   heavens,   have   also 
gaseous  or  nebular  tails. 

Meteors,  or  shooting  stars,  are  visible  most  any  clear 
night.  As  they  fall  and  sink  into  the  earth  their  heat  fuses 
the  sand  and  rocks.  Scientists  estimate  one  hundred  tons  of 
meteors  fall  on  the  earth  in  every  twenty-four  hours.  This 
raises  the  questions,  where  do  they  come  from,  why  do  they 
fall  to  the  earth  and  what  is  the  source  of  their  heat?  An 
answer  to  these  questions  will  no  doubt  solve  the  problem  as 
to  the  source  of  the  earth's  interior  heat. 

What  are  the  Nebular  and  Meteoritic  Theories? 

16.  The  older  astronomers  constructed  a  theory  known 
as  the  Nebular  Hypothesis,  which  supposes  the  earth's  origin 
was  due  to  nebulae  (star-gas)  collected  in  some  way,  which 
by  revolving  cooled  and  condensed  into  a  shining  star ;  in  the 
process  of  ages  it   further '  cooled  and  solidified,  ceased  to 
shine  and  became  like  the  moon. 

Later  scientists  conclude  the  earth  began  as  a  solid  body, 
perhaps  fragments  of  suns  and  stars,  collected  and  fused 


30      PRACTICAL  GEOLOGY  AND  MINERALOGY 

into  a  uniform  body  by  the  heat  generated  in  contact.  This 
is  called  the  Meteoritic  Theory,  and  inasmuch  as  the  earth 
is  slowly  adding  to  its  size  from  falling  meteors,  this  latter 
theory  is  both  plausible  and  reasonable:  hence  the  earth's 
interior  may  not  be  in  a  molten  state,  but  while  very  hot, 
remains  rigid  like  steel,  owing  to  the  pressure  of  the  outer 
crust. 

These  two  theories  named  are  not  in  direct  conflict,  as 
solid  and  gaseous  bodies  could  well  combine  in  accordance 
with  natural  laws. 

What  Practical  Use  are  These  Theories? 

1 7.  These  theories  are  interesting  and  cause  us  to  think, 
a  prime  necessity  in  the  study  of  any  science.     Heat  is  the 
great  force  in  causing  the  changes  in  the  earth  itself  as  well  as 
the  materials  that  compose  it,  and  a  knowledge  of  the  source 
of   this   heat   is   necessary   to   understand   the   formation   of 
minerals  and  ore  deposits,  which  follow  in  this  book.     It  has 
been  well  said  that,   "Each  theory  is  a  cord  on  which  to 
string  facts  that  otherwise  might  be  lost" ;  our  theories  may 
yet  be  thrown  away,  but  our  facts — never. 

What  are  the  Three  Kingdoms? 

18.  Everything  in  or  upon  the  earth  is  classed  under 
three  divisions,  known  as  the  Animal,  Vegetable  and  Mineral 
Kingdoms. 

THE  ANIMAL  KINGDOM  is  the  highest  and  last 
in  order  of  creation.  Animals  live  on  organized  matter,  that 
is,  on  other  animal  and  vegetable  life.  They  also  make  use 
of  mineral  matter,  but  seldom  as  a  food  product. 

THE  VEGETABLE  KINGDOM  is  more  closely  re- 
lated to  the  Mineral  Kingdom, — vegetation  lives  and  grows 


GEOLOGY  31 

on  minerals,  appropriating  these  from  the  Earth  and  from 
the  atmosphere.  The  Animal  and  Vegetable  are  termed 
organic  because  composed  of  organs  which  perform  certain 
functions,  while  the  Mineral  Kingdom,  having  no  organs, 
is  called  inorganic. 

THE  MINERAL  KINGDOM  has  always  existed.  It 
is  the  basis  of  all  life,  both  animal  and  vegetable.  When 
organic  matter  ceases  to  live,  it  changes  to  mineral.  The 
Animal  Kingdom  is  treated  under  the  Science  called  Zoology 
and  the  Vegetable  Kingdom  under  Botany,  but  the  three 
Kingdoms  are  so  related  that  the  changes,  at  least  from 
organic  to  mineral  matter,  deserve  some  mention  here. 

Myriads  of  animals  have  lived  and  died  since  creation. 
The  Earth's  crust,  including  the  sea  bottoms,  is  one  vast 
cemetery  in  which  lie  buried  the  carcasses  of  animals  that 
have  lived  and  died  in  all  past  ages.  Most  of  the  limestone 
rocks  are  formed  from  the  animal  fossils.  Myriads  of  the 
lowest  orders  of  sea  animals  secrete  slimes  and  sediments 
from  the  water  which  are  changed  to  rock.  (See  Quartz.) 

The  Vegetable  Kingdom  also  contributes  to  the  forma- 
tion of  minerals.  In  early  ages  while  the  earth  and  atmos- 
phere were  very  warm,  vegetation  grew  rank  and  dense; 
subsequent  changes  in  the  Earth's  crust  covered  up  this 
vegetation  and  as  a  result  we  have  mineral  coal  stored  up 
within  the  earth  for  unborn  generations.  Nature  has  also 
secreted  within  the  Earth,  mineral  oils,  from  the  combined 
remains  of  animal  and  vegetable  life. 

The  Mineral  Kingdom  then  is  at  once  the  beginning  and 
end  of  all  forms  of  matter  and  as  distinguished  from  organic 
matter  includes  everything  lifeless,  or  that  which  is  neither 
animal  nor  vegetable. 


32      PRACTICAL  GEOLOGY  AND  MINERALOGY 

The  Mineral  Kingdom  includes  Solids  like  rocks  and 
metals,  Liquids  like  water  and  Gases  like  oxygen,  hydrogen, 
nitrogen,  etc. 

The  remains  of  animal  and  vegetable  life — that  still  re- 
tain somewhat  their  life  form  of  structure,  are  termed  Fos- 
sils. This  subject  is  considered  under  a  separate  head  (See 
Fossils). 

Is  the  Earth's  Crust  Stable? 

19.  We  have  seen  that  the  Earth's  crust  is  uneven,  the 
elevations  being  called  hills  and  mountains  and  the  depres- 
sions called  valleys  and  basins.  These  conditions  exist  under 
the  sea  as  well  as  on  the  land.  We  have  also  learned  that 
the  Earth's  heat  generates  gases,  which,  according  to  natural 
laws,  will  seek  an  outlet  along  the  lines  of  least  resistance. 
In  other  words,  the  weakest  point  will  break  first,  just  as  a 
steam  boiler  will  burst  at  a  defective  place.  This  raises  the 
point — "Why  should  one  part  of  the  Earth's  crust  be  weaker 
than  another?" 

When  the  Earth  was  young  the  crust  was  thin  and  broke 
easily  to  permit  gases  and  molten  matter  to  escape.  As  the 
crust  cooled  it  grew  thicker,  but  pressure  of  the  seas,  and 
accumulated  sediments  made  a  denser  crust  than  elsewhere, 
and  not  so  easily  fractured.  When  we  consider  that  the  sea 
has  an  average  depth  of  over  two  miles  and  in  places  is  eight 
miles  deep,  the  water  pressure  is  enormous.  The  pressure  on 
sea  bottom  at  3000  fathoms  (about  3%  miles)  depth  is  three 
tons  to  the  square  inch.  From  these  facts  it  must  be  plain 
that  the  earth's  crust  is  not  stable,  and  that  there  is  now 
a  constant  upward  tendency  in  the  land  and  that  the  seas  are 
gradually  sinking. 


GEOLOGY 


33 


What  Proofs  are  There  of  Earth's  Movements  Today? 

20.  Proofs  of  the  raising  and  sinking  of  the  crust  are  to 
be  found  along  the  seashore  in  many  countries. 

The  columns  of  an  ancient  Roman  Temple  are  shown 
in  Fig.  3.  This  temple  was  built  on  the  seashore.  The 
ground  having  subsequently  sunk,  the  sea  invaded  the  temple 
long  enough  to  allow  marine  shells  to  burrow  into  the 
columns  some  yards  above  the  pavement.  Later  the  ground 


Fig.  3 


Temple  of  Serapis,  Pozzuoli 

was  uplifted  again  so  that  today  traces  of  sea  shells  are  seen 
about  midway  on  the  columns.  This  establishes  the  fact  of 
both  a  sinking  and  an  uplift  in  the  land  since  the  temple 
was  built.  Landmarks  on  the  coast  of  Sweden  show  the 
land  has  been  raised  four  feet  within  a  century,  while  the 
opposite  coast  of  Norway  has  sunken.  At  Sandusky,  Ohio, 


34      PRACTICAL  GEOLOGY  AND  MINERALOGY 

a  tract  of  land  growing  hay  eighty  years  ago  is  now  a  part 
of  the  lake.  The  land  on  the  east  coast  of  Lake  Michigan 
is  rising  and  the  west  coast  is  sinking.  These  are  positive 
proofs  within  the  memory  of  man,  and  when  it  is  considered 
that  a  century  as  we  now  measure  time  is  but  a  minute  in 


Fig.  4 


The  sea  covering  the  country  from  A 
toB. 


the  world's  history,  we  may  understand  the  movements  which 
seem  slow  to  us,  if  extended  over  millions  of  years,  would 
account  for  all  the  marvelous  changes  in  the  earth's  crust. 


Fig.  5 


Then  the  bottom  of  the  sea  rose  to  A'B'. 

In  Fig.  4  is  shown  a  section  of  the  earth's  crust,  the  sea 
covering  all  the  surrounding  country  from  A  to  B,  depositing 
regularly  and  slowly  its  materials  held  in  suspension  and  its 
shells ;  afterwards  the  bottom  of  the  sea  was  uplifted  as  shown 
in  Fig.  5,  and  the  section  A1  to  B1  with  all  its  solid  sedi- 
ments became  dry  land. 

Geologists  agree  that  since  the  appearance  of  man  on 


GEOLOGY 35 

earth,  the  continent  of  North  America  has  been  uplifted 
perhaps  by  the  pressure  of  the  waters  on  the  crust  under 
the  Atlantic  and  Pacific  Oceans,  which  pressure  doubtless 
has  also  gradually  deepened  the  ocean  beds. 

What  Proofs  Exist  that  Mountains  Have  Been  Uplifted 

21.  That  the  mountain  systems  now  shown  in  Geogra- 
phies have  not  always  existed  is  now  generally  accepted,  but 
it  will  be  well  to  see  if  the  evidence  supports  such  belief. 

(a)  Upon  many  mountain  ranges  of  the  world,  marine 
shells  have  been  found,  sometimes  two  miles  above  sea  level. 
How  did  they  get  there?     Two  ways  are  possible.     First, 
they  have  been  carried  there  by  living  creatures;  the  shells 
are  far  too  numerous  and  the  sea  usually  too  distant  to  make 
this  appear  reasonable.     A  better  explanation  is  that  these 
mountains  once  lay  in  the  bottom  of  the  sea  and  were  up- 
lifted by  a  series  of  violent  upheavals,  which  carried  the  sea 
shells  along  to  these  great  heights. 

(b)  The  structure  of  high  mountain  ranges  as  compared 
with  lower  chains  and  hills  furnish  further  evidence. 

Anyone  familiar  with  the  character  of  high  mountains, 
knows  that  they  contain  more  fractures,  fissures  and  faults 
than  the  lower  hills.  The  reason  for  this  is  not  difficult  to 
see.  Hills  were  either  formed  by  a  single  heave  or  eruption, 
when  the  earth's  crust  was  soft  and  easily  broken,  or  were 
formed  by  sedimentary  deposits  and  compressed  by  ponder- 
ous masses  of  overlying  earth,  and  then  uplifted. 

Hence  it  is  that  building  stone,  free  from  cracks  and  of 
large  close-grained  blocks,  are  quarried  only  in  the  lower 
hills,  and  mountains ;  the  high  mountains  being  formed  after 
the  crust  became  rigid,  it  required  giant  forces  to  fracture 
the  crust,  but  once  an  opening  was  made,  a  succession  of 


36      PRACTICAL  GEOLOGY  AND  MINERALOGY 

heaves  or  eruptions  took  place,  carrying  the  mass  to  tower- 
ing heights;  these  on  cooling  were  again  subjected  to  the 
eruptive  forces  that  left  them  in  the  broken  up  condition  we 
find  them  today,  unfit  for  any  structural  purpose. 

The  high  mountains  are  mainly  crystalline  rocks  like 
granite  and  contain  no  fossils,  which  we  shall  later  see  is 
convincing  evidence  that  they  were  forced  up  from  great 
depths  in  the  earth. 

What  Relation  do  Mountains  Sustain  to  Mineral 
Deposits? 

22.  Look  at  the  map  of  most  any  continent  and  you  will 
see  that  the  mountains  parallel  the  sea  coast.    The  mountain 
ranges  constitute,  or  rather  fill  immense  faults,  in  the  earth's 
crust  with  fire  formed  rocks.     The  principal  mineral  belts 
of  the  world,  as  well  as  the  vein-fissures,  usually  follow  the 
general  course  of  the  mountains.    These  facts  seem  to  explain 
the  connection  of  mineral  bodies  with  mountains  rather  than 
with  valleys  and  basins;  the  faulted  and  fractured  condition 
of  eruptive  rocks,  produce  the  conditions  favorable  to  the 
formation  of  mineral  bodies  of  the  precious  metals. 

What  Crust  Changes  are  Due  to  Action  of  Air 
and  Water? 

23.  The  atmosphere  surrounding  the  Earth  and  extend- 
ing upwards  for  several  miles,  is  composed  of  gases  and  other 
elements,  which  cannot  be  fully  explained  here.     It  is  suffi- 
cient now  to  say  that  the  action  of  these  elements  in  the  air, 
on  the  exposed  surface,  tends  to  break  up  and  disintegrate 
rocks  of  all  kinds  by  a, process  caled  corosion  or  weathiring, 
which  literally  means  eating-away  or  into,  as  seen  in  the 
common  example  of  iron  rusting  from  exposure  to  air. 


GEOLOGY 37 

The  action  of  water  on  the  earth's  crust  is  known  as 
erosion,  which  means  a  wearing  away.  It  is  an  old  saying 
that  "The  constant  dropping  of  water  will  wear  away  the 
hardest  stone,"  and  when  we  consider  the  millions  of  years, 
the  rains  have  beaten  down  on  the  earth's  crust,  we  can 
understand  somewhat  of  the  wearing  process  due  to  the 
action  of  the  water. 

What  Other  Forces  Assist  Air  and  Water? 

24.  Two  other  forces  unite  with  air  and  water  to  pro- 
duce changes : 

(a)  GRAVITY.     This  is  the   force   that   holds  the  seas 
in  their  beds,  draws  down  the  rain  from  the  clouds,  and 
keeps  the  water  moving  on  and  on,  until  it  reaches  sea  level, 
only  to  be  changed  into  vapor,  rise  again,  form  new  clouds 
and  fall  again  as  rain  or  snow. 

(b)  THE    RADIANT    ENERGY    OF    THE    SUN    causes 
the   water    upon    the    earth   to  vaporize,     rise   and    form 
clouds.     The  snows  that  fall  on  the  mountains  melt  under 
the  sun's  rays  and  start  the  water  tearing  downward  on  its 
way  to  the  seas.     The  rocks  of  the  Earth  are  porous  and 
absorb  water ;  on  cold  nights  and  in  winter  the  crust  freezes, 
o^ly  to  be  followed  by  melting  from  the  sun's  heat.     This 
alternate  expansion  due  to  heat,  and  contraction  due  to  cold, 
is  a  most  powerful  factor  in  breaking  up  the  rocks  of  hills 
and  mountains. 

(c)  The    Earth    contains   much    mineral    coal    and    oil 
which  is  mainly  carbon.     This  once  existed  combined  with 
the  gases  of  the  atmosphere  and  must  have  assisted  largely  in 
the  changes  that  have  been  made  in  the  earth's  crust. 

All  these  Geologic  forces  named,  acting  together  wear  and 


Fig.  6 


GEOLOGY  .  39 

tear  away  the  elevated  portion  of  the  crust  and  spread  out 
the  materials  in  the  valleys  and  basins  below,  forming  sedi- 
ments that  are  compressed  into  dense  rocks  by  accumulated 
material,  which  make  up  three-fourths  of  the  crust  as  we 
know  it  today. 

These  changes  are  taking  place  under  our  very  eyes 
today,  but  there  is  strong  reason  to  believe  that  in  the  past 
ages  these  forces  were  more  violent  and  the  changes  more 
rapid. 

What  are  Glaciers?  .  What  Changes  do  They  Produce? 

25.  GLACIERS  are  masses  of  snow  and  ice  melted 
and  consolidated.  They  exist  today  in  high  mountains  in 
Europe,  in  Canada,  and  in  the  northwest  United  States.  At 
the  equator  the  line  of  permanent  snow  is  16,000  feet  above 
sea  level ;  towards  the  poles  this  line  grows  lower  and  lower, 
until  the  Arctics  are  reached,  where  the  "snow-line"  is  the 
sea  level. 

The  high  mountains  in  Switzerland  furnish  the  best 
example  of  glaciers  and  their  action  today.  There  the  snow 
accumulates  in  winter  to  great  depths ;  as  summer  approaches, 
under  the  action  of  the  sun's  rays,  the  snow  melts  in  day- 
time and  freezes  into  ice  at  night.  The  Earth  and  rocks 
underneath  become  loosened  from  thaws,  and  by  pressure  of 
mass  above.  This  permits  the  glaciers  to  move  slowly  down 
the  mountain  sides,  producing  a  scouring,  grinding  action  of 
the  underlying  stones,  polishing  and  cutting  stria  (grooves) 
in  their  surfaces  like  that  shown  in  Fig.  6. 

Throughout  Europe  and  in  North  America,  north  of  the 
mouth  of  the  Ohio  river,  rocks  are  found  with  polished 
surfaces  and  marks  (stria)  similar  to  those  produced  by 


40      PRACTICAL  GEOLOGY  AND  MINERALOGY 

Glaciers  in  Switzerland,  which  seems  to  point  to  the  same 
Glacial  origin. 

On  the  west  coast  of  Greenland  is  a  Glacier  1,200  miles 
long  and  2,000  feet  high.  Some  of  these  vast  ice  masses 
become  detached  in  warm  weather,  float  to  the  southward 
and  are  slowly  dissolved  by  the  warmer  ocean  currents. 
These  glaciers  often  have  masses  of  stone  frozen  in  them. 
In  floating  the  greater  mass  is  beneath  the  water,  and  in 
coming  in  contact  with  rocks  or  an  exposed  cliff,  grind  and 
mark  their  surfaces  in  such  a  manner  as  to  leave  no  doubt  as 
to  the  cause. 

What  Evidence  u  There  of  Glacial  Action  on  the 
Earth's  Crust? 

26.  We  know  that  the  Arctic  regions  once  had  a  warm 
climate,  as  proven  by  vast  coal  deposits  and  bones  of 
tropical  animals  now  found  there,  and  that  the  land  was 
repeatedly  baptized  by  water.  In  the  course  of  ages,  the 
conditions  changed,  the  North  Temperate  Zone  was  deluged 
by  ice  drifting  down  from  the  Arctics.  This  period  is 
known  as  the  Glacial  Age.  (See  Quar ternary  Period.) 

The  proofs  of  the  Glacial  Age  are  the  finding  of  the  bones 
of  Polar  animals  in  the  Temperate  Zone  and  by  the  exist- 
ence of  great  areas  of  boulders  whose  surfaces  are  polished 
and  scratched  just  as  glacial  action  results  today.  Fig.  7 
shows  a  field  of  boulders  thus  formed. 

The  whole  of  North  America  east  of  the  Rocky  Mount- 
ains, and  north  of  the  36th  parallel,  shows  unmistakable 
evidence  of  the  ''northern  drift."  The  great  Mississippi 
Valley  region  has  water  formed  rocks  as  its  natural  bed. 
On  top  of  these  are  fire-formed  rocks,  and  as  there  are  no 


GEOLOGY  41 


evidences  of  these  having  been  forced  up  from  below,  we 
must  look  to  other  causes.  Some  places  this  drift  rock  is 
only  a  slight  covering,  in  other  places  it  is  piled  up  into  high 
hills,  and  ridges.  These  fire-formed  stones  are  all  more  or 
less  rounded  and  polished,  varying  in  size  from  cobble  stones 
to  boulders  weighing  many  hundred  tons. 

The  parent  ledges  from  which  these  stones  came  are 
always  found  to  the  northward,  sometimes  only  a  few  miles, 
but  often  hundreds  of  miles  distant.  The  streets  of  Cin- 
cinnati are  paved  with  stones  believed  to  have  been  trans- 
ported by  Glaciers  from  the  region  of  the  Great  Lakes. 
Native  copper  from  Lake  Superior  Region  is  scattered  over 
half  dozen  states  to  the  southward. 

These  Glacial  Boulders  have  parallel  grooves  or  stria 
and  the  sides  of  hills  and  mountains  of  that  region  show  the 
same  polishing  and  grooving  action,  on  every  side  except  the 
south.  This  seems  to  prove  the  drift  was  from  the  north. 
These  proofs  leave  no  doubt  that  there  was  a  Glacial  Period 
and  these  changes  were  due  to  the  action  of  Glaciers. 

What  Was  the  Cause  of  This  Glacial  Drift? 

27.  Geologists  fully  agree  that  there  was  a  Glacial 
Period,  but  do  not  altogether  agree  as  to  the  causes.  The 
weight  of  authority,  however,  inclines  to  the  theory  that  the 
earth's  crust  in  the  Arctic  Regions,  was  uplifted.  It  is  also 
probable  that  a  corresponding  depression  was  caused  in  the 
crust  to  the  southward.  In  accordance  with  the  laws  of 
gravitation,  this  sea  of  ice  would  seek  a  lower  level  and 
move  along  the  lines  of  least  resistance,  which  would  have 
been  through  the  great  central  basin.  The  Old  World  suf- 
fered a  Glacial  Period  also,  which  seems  to  show  the  Arctic 
uplift  was  the  main  cause  of  the  Glacial  Period. 


42      PRACTICAL  GEOLOGY  AND  MINERALOGY 

Was  the  Pacific  Coast  Affected  by  Glaciers? 

28.  The  Northern  Drift,  coming  after  the  Rocky  Moun- 
tains were  elevated,  they  formed  a  natural  barrier,  confining 
the  Glacial  ice  to  the  eastward.     However,  Geologists  be- 
lieve the  temperature  of  the  western  portion  of  the  continent 
must  have  been  very  cold  during  this  period  and  that  Glaciers 
were   formed   throughout   the   higher   Rockies   and   Sierras, 
much  as  are  now  formed  in  the  Alps.     In  fact,  Glaciers  that 
now  exist  in  Canada,  and  in  the  northwest  United  States, 
probably  had  their  origin  in  a  former  epoch. 

Throughout  the  Rockies  and  Sierras,  fields  of  boulders 
may  be  seen  with  all  the  evidence  of  Glacial  marking  and 
polishing. 

These  Sierra  Glaciers  in  melting,  formed  torrents  of 
water,  which,  rushing  down  the  mountain  sides,  denuded 
great  areas.  The  process  of  erosion  broke  up  the  auriferous 
(Gold)  rocks,  concentrating  their  gold  contents  into  the 
rich  placers  that  excited  the  world  in  1849  and  still  yield 
up  their  millions  yearly.  The  Gold  Placers  of  Alaska  un- 
doubtedly had  their  origin  in  a  similar  way  due  to  glacial 
action.  (See  Fig.  49.) 

What  are  Known  as  the  Geologic  Ages? 

29.  The  Age  of  the  Earth  in  years  or  centuries,  is  un- 
known.    Some  Geologists  have  attempted  to  fix  the  period 
of  time  since  Creation  by  taking  the  record  of  changes  since 
history  began  and  tracing  back  to  the  beginning,  but  all  such 
estimates  run  into  the  millions  of  years,  and  being  merely 
guesses,  serve  no  useful  purpose. 

Although  we  may  not  say  how  old  the  Earth  is,  nor 
even  the  age  of  a  single  strata  in  the  crust,  yet  we  may 


GEOLOGY 


43 


correctly  say  that  one  strata  is  older  or  younger  than  another, 
from  the  evidence  showing  its  earlier  or  later  formation.  To 
illustrate,  a  crystallized  rock,  having  no  sign  of  animal  or 
vegetable  remains,  underlying  another  rock  strata,  containing 
fossils,  we  may  safely  say  the  under  rock  is  the  older,  and 
the  upper  rock  the  younger,  without  attempting  to  give  the 
actual  age  of  either. 

In  Fig.  8  is  shown  a  section  of  the  earth's  crust  as  the 
rocks  would  appear  in  their  natural  position,  the  younger 
above  and  the  older  below.  The  lower  strata,  A  and  B,  are 
igneous  (fire  formed)  rocks  without  fossils,  and  rock  strata 

Fig.  8 


F.  Quaternary. 

E.  Tertiary. 

1      Rocks 

D.  Secondary. 

/      origin 
_A    (Fossils). 

0.  Primary. 


Crystalline  rocks, 
igneous  origin 
(no  Fossils). 


C,  D,  E  and  F  are  aqueous   (water  formed)   and  contain 
fossils. 

If  the  rocks  were  always  found  in  the  position  shown, 
the  Geologist's  task  would  be  easy,  but  as  a  matter  of  fact 
this  is  seldom  the  case.  For  example — granite  is  one  of  the 
primary  rocks,  that  is,  if  you  should  dig  down  through  the 
successive  formations,  the  last  rock  encountered  would  likely 
be  granite.  Being  the  foundation  rock  of  the  crust,  it  would 
necessarily  be  the  oldest. 

Our  high  mountain  ranges  are  largely  granite,  which 
often  spreads  out  and  overlies  all  water  formed  rocks.  In 


44      PRACTICAL  GEOLOGY  AND  MINERALOGY 

such  a  case  the  granite  would  be  the  younger,  notwithstand- 
ing it  contained  no  fossils.  The  evidence  being  conclusive 
that  the  granite  was  forced  through  a  crack  in  the  crust  after 
the  other  rocks  were  formed,  while  the  unnatural  position  of 
the  granite  would  put  it  in  the  infant  class  by  comparison. 

In  the  formative  periods  of  the  Earth's  history,  there  was 
a  contest  between  fire  and  water,  the  latter  finally  gaining 
the  mastery.  While  the  conflict  was  raging,  the  crust  re- 
ceived repeated  baptisms  of  water,  the  Geologic  forces  carried 
the  eroded  and  powdered  rocks  from  the  heights  to  the  basins 
below,  forming  sedimentary  rocks. 

These  strata,  or  layers,  and  their  fossil  contents,  form 
what  are  called  the  Geological  Ages  of  the  Earth's  crust.  It 
is  thus  that  history  is  indelibly  written  in  the  rocks  so  that 
man  may  learn  to  read  it  as  he  would  the  chapters  of  a 
printed  book. 

How  Do  Fossils  Record  Earth's  History? 

30.  The  Earth's  crust  has  been  undergoing  changes  from 
the  beginning,  and  the  final  chapters  in  its  history  are  not 
yet  written. 

The  origin  of  the  Earth,  according  to  the  theories  (Par. 
6),  resulted  in  a  globe  of  fairly  even  surface.  The  contrac- 
tion due  to  cooling,  produced  earthquakes  and  enormous 
cracks  in  the  crust,  through  which  flowed  molten  matter  to 
form  hills  and  mountains.  The  geologic  forces  disintegrated 
these  elevated  portions  and  the  pulverized  rock  dust  was 
washed  down  by  flooded  water,  forming  into  strata  in  the 
basins.  These  were  compressed  and  baked  by  the  Earth's 
heat  into  the  sedimentary  rocks. 

These  strata  were  not  formed  over  the  entire  earth  at  the 


GEOLOGY  45 

same  time  for  the  reason  that  when  one  continent  was  ele- 
vated, another  was  covered  with  the  sea.  This  accounts  for 
the  absence  of  a  strata  in  some  countries.  Often  a  strata 
found  in  one  country  will  have  a  corresponding  strata  in 
another  country  of  a  very  different  material,  the  presence 
of  the  same  fossils  being  the  only  connecting  link.  To  illus- 
trate:— The  limestone  strata  of  North  America  corresponds 
closely  in  age  with  the  chalk  strata  of  Western  Europe. 

Then  there  are  salt  water  fossils  and  fresh  water  fossils; 
that  is,  fossils  of  land  animals  and  sea  animals,  fossils  of 
sea  plants  and  land  plants.  This  raises  the  question:  How 
can  the  fossils  be  distinguished?  This  largely  belongs  to  the 
sciences  of  Zoology  and  Botany,  but  there  are  certain  basic 
principles  that  aid  us  in  this  matter,  which  will  have  brief 
notice  here. 

If  a  rock  contains  sea  animal  fossils,  it  proves  that  the 
rock  crust  was  beneath  the  sea  at  the  period  of  formation. 
Similarly  the  presence  of  land  animal  or  vegetable  fossils 
proves  that  portion  of  the  crust  was  elevated  while  the  rock 
was  being  formed. 

Thus  the  fossils  furnish  the  link  to  unite  the  parts  of  the 
geologic  chain  that  encircles  the  Earth.  The  fossils  are  called 
the  "Medals  of  Creation,"  which  tell  the  successive  creations 
of  animal  and  plant  life,,  just  as  the  coins  of  a  buried  city 
unknown  to  history  tell  the  relative  age  and  place  of  such  a 
city  in  the  world's  history.  Each  formation  has  its  peculiar 
fossils  and  the  naturalist  is  often  able  to  restore  the  form  of 
a  plant  or  animal  and  determine  its  habits  by  a  fragment  of 
a  tooth  or  bone.  One  naturalist  was  able  to  restore  a  fish 
and  classify  it  from  a  single  scale  fossil. 


46      PRACTICAL  GEOLOGY  AND  MINERALOGY 

There  are  no  sharply  defined  lines  separating  the  geologic 
ages.  They  fade  into  each  other  as  the  plain  blends  into 
the  mountain,  yet  each  as  a  whole  has  its  peculiar  character- 
istics, so  that  those  trained  to  this  work  seldom  have  any 
difficulty. 

How  Is  the  History  of  the  Earth's  Crust  Divided? 

31.  By  referring  to  the  Geological  Section,  page  48, 
you  will  see  the  rock  strata  arranged  in  the  order  they  were 
formed.  The  age  increases  from  the  surface  downward, 
but  this  perfect  horizontal  arrangement  is  rare,  as  the  Earth 
movements  have  tilted  up  the  various  formations  at  different 
angles.  Intrusion  of  igneous  matter  from  below  also  causes 
endless  twisting,  folding  and  dislocation  of  rock  formations. 

Geologists  divide  the  history  of  the  crust  into  Eras, 
according  to  the  animal  and  vegetable  life  that  then  existed, 
as  follows: 

(1)  Azoic  Era  (without  life). 

(2)  Paleozoic  Era  (Ancient  Life). 

(3)  Mesozoic  Era  (Middle  Life). 

(4)  Cenezoic  Era    (Recent   Life). 

These  Eras  are  divided  into  what  are  called  ages,  accord- 
ing to  their  principal  fossils,  as  follows: 

(A)  Silurian   Age    (Age   of    Mollusks). 

(B)  Devonian  Age  (Age  of  Fishes.) 

(C)  Carboniferous  Age  (Age  of  Coal  Plants). 

(D)  Age  of  Reptiles. 

(E)  Age  of  Mammals. 

These  Ages  are  subdivided  into  Periods,  to  mark  the 
character  of  rocks  formed,  viz:  (a)  Crystalline  Rocks;  (b) 
Primary  (1st)  Rocks;  (c)  Secondary  (2nd)  Rocks;  (d) 


GEOLOGY  47 

Tertiary    (3rd)    Rocks;      (e)   Quarternary      (4th)    Rocks. 
(See  Geologic  Section,  page  48.) 

What  Constitutes  the  Azoic  Era? 

32.  The  Earth's  interior  being  very  hot,  no  regular 
well-defined  formation  can  exist  there.  As  this  mass  comes 
in  contact  with  the  cooler  crust,  it  crystallizes  and  takes  on 
a  form  that  permits  classification.  The  word  Azoic  means 
without  life  and  applies  to  rocks  so  highly  heated  as  to  make 
life  impossible  in  them. 

It  seems  certain  that  no  part  of  the  original  crust  exists 
today.  Nature's  forces  have  changed  and  moulded  it  over 
and  over  again  in  the  process  of  ages.  The  oldest  rocks 
known  today  belong  to  the  Azoic  Era,  such  as  Granite, 
Syenite,  Gneiss,  Porphyry,  Talc,  etc.  The  most  valuable 
deposits  of  iron  ore  like  those  of  Michigan,  Pennsylvania, 
Alabama,  Missouri  and  Colorado,  are  found  in  the  Azoic 
Rocks. 

A  glance  at  the  Geologic  Sketch  (page  20)  in  the  front 
of  the  book,  shows  the  Azoic  Rocks  of  North  America, 
marked  No.  1,  on  a  light  mottled  background. 

Note  also  the  region  about  Lake  Superior,  the  richest  iron 
and  copper  region  of  the  world,  is  in  these  ancient  rocks. 
North  of  the  Great  Lakes  this  formation  extends  northeast 
to  the  Atlantic,  thence  southwest  into  the  United  States  along 
the  Appalachian  mountains. 

The  Azoic  Rocks  are  devoid  of  both  animal  and  vegetable 
fossils,  and  are  classed  as  crystalline,  being  very  favorable 
for  deposits  of  metals  and  minerals. 


SECTION 


PER- 
IOD 


IFORM 
I  TION 


CHARACTER  OF  ROCKS 


RE- 
CENT 


J 


1 

3 


Alluvium,  Clay,  Pebbles, 
Conglomerate,  Etc. 


Basalt,  Andesite,  Lava. 
Sandstone,  Shale  and  Clay. 


Rhyolite,  Volcanic  and 
Granite  Detritus. 


Soft  Sandstone,  Shale,  Lime- 
stone, Lignite  Coal,  Fire- 
clay, Etc. 


Trap  Rocks,  Limestone, 
Quartzite,  Conglomerate, 

Metamorphic- Sandstones, 
Eruptive  Granite. 


Blue-Limestones, 
Gypsiferous  Shales, 
Bituminous  Coal  Beds, 
Grit  Conglomerates,  Etc. 


Magnesian  Limestone, 
Red  Sandstone,  Shale,  Etc. 


Limestone,  Hard  Sandstone, 
Dolomite,  Shale,  Etc. 


Slate,  Quartzite,  Hard  Sand- 
stone, Marble,  Etc. 


Gneiss  Mica-Schist, 
Quartzite  Granite, 
Porphyry,  Syenite,  Etc. 


GEOLOGY  49 

What  Marks  the  Paleozoic  Era? 

33.  Refer  again  to  the  Chart,  page  48,  and  note  that  this 
Era  is  divided  into  ages  known  as  Cambrian,  Silurian, 
Devonian  and  Carboniferous.  The  names  of  these  sub- 
divisions have  been  given  them  to  mark  the  changes  in  animal 
and  vegetable  life — as  evidenced  by  the  fossil  remains. 

Cambrian  Age.  This  takes  its  name  from  Cambria,  the 
Latin  for  Wales,  where  the  rocks  lying  next  to  the  crystal- 
line were  first  noted.  It  is  also  called  "Lower  Silurian"  by 
some  Geologists.  The  first  distinctive  animal  fossils  appear  in 
the  Cambrian  Age. 

The  rocks  the  Cambrian  Age  began  to  form  from  the 
sediment  or  muddy  waters  into  shales.  These  with  added 
pressure  and  heat  were  changed  into  Slates.  Quartzsite 
made  its  appearance.  Limestones  were  crystallized  into 
marble.  The  Cambrian  formation  extends  along  the  eastern 
base  of  the  Appalachians.  It  crops  out  at  various  points  west 
of  the  Missouri  River.  The  Lead-Zinc  ores  of  Illinois,  Wis- 
consin and  Missouri  are*  found  in  the  limestones  of  this 
period.  Volcanic  disturbances  in  the  region  of  Lake  Superior 
tilted  up  the  primitive  rocks  and  formed  a  bed  for  the  Lake. 
Fissures  there  formed  were  filled  with  native  copper,  the 
richest  in  the  world. 

The  Black  Hills  of  Dakota,  and  sections  of  country  west 
of  the  Rockies  also  belong  to  this  period.  Next  to  the  Azoic 
rocks,  those  of  the  Cambrian  are  the  most  favorable  for 
minerals,  especially  when  intruded  by  Eruptive  Rocks. 

No  land  animals  had  yet  appeared,  but  the  seas  swarmed 
with  coral  insects  during  this  period. 


50      PRACTICAL  GEOLOGY  AND  MINERALOGY 


Fig  9. 


What  Distinguishes  the  Silurian  Age? 

34.  This  also  takes  the  name  from  a  tribe  of  Britons, 
called   Silures,   where   the    formation   was   first    discovered. 
The  salt  beds  of  North  America  were  formed  in  this  period, 

due  to  the  evaporation  of  ocean 
water  that  formerly  covered  the 
land.  Magnesian  Limestone  (Dolo- 
mite) and  hard  compact  Sandstones 
make  their  first  appearance.  The  Si- 
lurian Age  is  known  as  the  "Age  of 
Mollusks,"  those  soft  bodied  animals 
having  shells  like  oysters,  whose  fos- 
sils are  well  preserved  in  many  of  the 
rocks  of  this  Age.  (See  Fig.  9.) 
Fossil  oystew.  Some  important  mines  in  Arizona 

and  Nevada  are  found  in  rocks  of  this  age. 

How  Can  We  Tell  the  Devonian  Rocks? 

35.  This   Age   takes   its   name    from    Devon,    England, 
where  the  formation  is  clearly  developed.    The  rocks  of  this 

Fig.  10. 

A, 
fl 


Ideal  section  illustrating  structural  relations  southeast  of  Fort  Bowie,  Ariz, 
age  are  red  sandstones,  shale,  slate  and  magnesian  limestones. 
It  is  also  called  the  "Age  of  Fishes,"  the  fossils  of  which  first 


GEOLOGY  51 

appear.  Vegetable  fossils,  flags,  rushes  and  shrubs  are  also 
noted.  A  good  portion  of  the  Ohio  Valley  was  covered  with 
dense  marshes,  and  climatic  conditions  were  such  as  to  pro- 
duce a  very  rank  growth  of  vegetation  during  this  and  the 
preceding  Ages. 

The  rocks  of  this  period  carry  ore  bodies  in  connection 
with  intrusive  sheets  of  porphyry.  (See  Geological  Sketch.) 

What  Is  Known  of  the  Carboniferous  Age? 

36.  This  Age  is  so  named  from  the  abundance  of  coal 
formed  in  its  times.  The  element  carbon  forms  the  frame- 
work of  all  plants.  When  vegetation  dies  and  remains 
exposed  to  the  atmosphere,  it  decomposes,  rots  as  we  common- 
ly say,  and  forms  vegetable  mould  or  soil.  However,  when 
vegetation  is  covered  up  and  removed  from  the  action  of  the 
air,  it  is  preserved,  and  when  accumulated  debris  makes 
pressure  great,  the  water  is  squeezed  out  and  it  forms  into 
the  mineral  we  call  coal.  The  longer  it  is  b"ried  and  the 
greater  the  pressure,  the  better  the  coal.  The  peat  bogs  toda> 
are  simply  Coal  in  the  first  stages.  ( See  Fig.  11.) 

Fig.  ||  Scientists  conclude  that  the  pres- 

ence of  large  amounts  of  carboni^ 
acid  in  the  atmosphere  and  the 
combined  heat  of  the  sun  and  the 
earth's  crust,  tended  to  produce  a 
dense  tropical  growth. 

No  air-breathing  animal  had  yet 
appeared  as  they  could  not  exist 

A    fragment  of    coal  i  111-1 

bearing    the    impression  of  a  HI  SUCH  an  atmosphere,  laden  With 

fern-leaf. 

the  deadly  carbonic  acid.     An  all 
wise  Providence  seemed  to  have  had  two  objects  in  view, — 


52      PRACTICAL  GEOLOGY  AND  MINERALOGY 

first  to  purify  the  air  by  the  growth  of  very  dense  vegetation, 
and  second  to  store  away  fuel  for  future  generations  of  men. 

The  North  American  Continent,  that  had  been  rising 
slowly  from  beneath  the  sea,  now  began  to  sink,  carying  along 
the  dense  vegetable  growth  of  preceding  ages.  Sedimentary 
matter,  from  the  heights  was  washed  down  covering  it 
deeper  and  deeper  until  the  buried  vegetation  was  thousands 
of  feet  beneath  the  sea. 

The  principal  coal  beds  of  North  America  had  their 
origin  in  the  Carboniferous  Age.  An  idea  of  the  vegetable 
growth  may  be  had  from  the  thickness  of  the  Mammoth 
Coal  Vein  in  Pennsylvania  of  thirty  feet  and  a  vein  of  coal  in 
Nova  Scotia  40  feet  thick.  This  coal  underlies  sandstone 
mainly,  and  as  this  is  known  to  be  an  aqueous  or  water  rock, 
we  have  additional  proof  that  this  coal  was  formed  by  buried 
vegetation. 

In  Western  North  America,  this  Age  is  marked  by 
gypsum  shales  and  blue  limestones.  The  western  coals,  espec- 
ially the  softer  varieties,  were  not  formed  until  a  later  period. 
The  Carboniferous  rocks  are  not  favorable  for  metallic  ore 
bodies. 

What  Characterizes  the  Mesozoic  Era? 

37.  Mesozoic  means  middle  life,  which  began  a  new 
cycle  in  the  Earth's  history.  A  higher  order  of  animal,  the 
reptile,  now  appears,  the  fossils  of  which  distinctly  mark  the 
dividing  line  between  this  and  preceding  age.  The  Mesozoic 
is  usually  divided  into  three  periods,  viz: 

(1)  Triassic  (Triple),  so  named  from  three  distinct 
groups  found  in  Germany. 


GEOLOGY  53 


(2)  Jurassic,   so   named   from   the   Jura   Mountains  in 
Switzerland. 

(3)  Cretaceous  (Chalk). 

The  first  two  are  not  distinct  in  North  America,  so 
are  usually  classed  under  the  compound  name  Jura-Trias. 
During  this  age  the  Carboniferous  area  is  again  uplifted  from 
its  long  burial  under  the  seas.  The  central  portion  of  the 
continent  was  pushed  up ;  rock  making  advanced  towards  the 
Atlantic  on  the  east,  the  Gulf  on  the  south  and  towards  the 
Rockies  on  the  west. 

In  the  old  world,  during  this  period,  the  salt  deposits  of 
England,  Poland  and  Spain  had  their  origin.  In  North 
America  this  period  was  characterized  as  one  of  violent 
upheavals  and  perhaps  terrific  convulsions  of  nature,  causing 
such  stupendous  mountain  ranges  as  the  Sierras  to  be  lifted 
above  the  interior  sea.  Everywhere  trap  dikes  and  ridges 
attend  this  formation.  The  proof  of  this  is  that  the  adjacent 
sandstones  were  baked  by  heat,  the  layers  uplifted  by  escaping 
steam  and  the  fissures  often  filled  by  crystallized  minerals. 
The  Gold-bearing  rocks  of  the  Pacific  Coast  are  in  what  is 
known  as  the  Jura-Trias  Belt,  extending  from  Alaska  to 
Central  America  and  having  a  width  of  300  miles  in  places. 
These  rocks  are  found  as  far  east  as  the  Rockies,  but  are  not 
so  distinct  as  in  the  Sierras. 

During  this  period  such  giant  fissures  as  the  Mother  Lode 
in  California  were  formed  and  filled  with  mineralized  matter. 
These  fissures  generally  follow  the  trend  of  the  mountain 
ranges  or  run  parallel  thereto.  The  cross-veins  are  of  a  later 
period  and  not  so  well  mineralized. 


54      PRACTICAL  GEOLOGY  AND  MINERALOGY 

What  Peculiarity  Has  the  Cretaceous  Period? 

38.  This  period  takes  its  name  from  Greta,  Latin  for 
chalk,  and  hence  is  called  the  Chalk  Period.     It  is  very  dis- 
tinct in  the  Old  World.     In  North  America,  however,  the 
formation  is  a  mixture  of  chalk  and  sand,  forming  what  are 
called  soft  sandstones,  many  of  which  can  be  dug  out  of  the 
earth  with  a  spade  and  rubbed  to  pieces  in  the  hand. 

The  presence  of  the  same  fossil  shells,  as  the  chalk  forma- 
tion of  England  and  France,  serves  to  identify  it  as  belonging 
to  the  same  Cretaceous  period. 

Lignite  (Wood)  coals  of  the  Rocky  Mountain  and 
Pacific  Coast  as  well  as  the  Quicksilver  deposits  of  California, 
are  all  found  in  the  Cretaceous  rocks.  This  formation  ex- 
tends along  the  eastern  base  of  the  Appalachians  from  New 
York  to  Mississippi;  from  Texas  northward  along  the 
eastern  base  of  the  Rockies,  and  in  places  extending  across 
their  slopes  as  well  as  along  the  western  base  of  the  Sierras. 
The  rocks  of  this  period  are  not  good  ore  bearers,  but  are 
more  noted  for  Coal  and  Oil. 

What  Is  the  Cenozoic  Age? 

39.  Previous  to  this  era  all  animals  lived  in  the  water. 
A  new  order  of  animals  now  appear,  which  suckle  their 
young,  hence  it  is  called  the  "Age  of  Mammals."  The  fossils 
of  forest  trees  first  appear  in  the  rocks  of  this  age. 

In  the  Old  World,  this  era  is  divided  by  Geologists  into 
several  periods,  but  these  distinctions  are  not  clearly  defined 
in  North  America,  hence  these  will  be  classed  under  the 
common  names  of  Tertiary  (Third)  *nd  Quarternary 
(Fourth)  Periods. 


GEOLOGY 55 

Tertiary  Period 

40.  A  glance  at  the  Map  (Fig.  12)  will  show  Geological 
conditions  as  they  appear  in  this  period  of  North  America. 
The  white  shows  the  land,  and  the  shaded  portions,  the  con- 
tinental crust  still  covered  by  water. 

Fig.  12 


Map  of  North  Anjerica  in  the  Tertiary  Period 

Small  veins  of  lignite  coal  were  formed  during  this  period, 
but  they  are  of  little  importance.  No  great  mountain 
uplifts  occurred  as  during  the  Jura-Trias  period.  The 
older  rocks  underwent  a  change  (Metamorphosis),  that  is 
the  igneous  rocks  were  decomposed  and  formed  into  sedi- 


56      PRACTICAL  GEOLOGY  AND  MINERALOGY 

mentary  rocks,  while  some  of  the  stratified  rocks  were  meta- 
morphosed by  pressure  and  internal  heat.  What  is  called 
Conglomerate  Rock,  composed  of  igneous  and  aqueous  rocks, 
pebbles,  etc.,  were  cemented  together  with  lime  matter  during 
this  period.  The  formation  of  shales  and  clays  also  con- 
tinued during  this  period.  Many  mountain  valleys  received 
a  top-dressing  of  vegetable  detritus  from  adjacent  hills, 
forming  arable  land. 

The  most  distinctive  feature  of  this  period  was  the  for- 
mation of  Basalts  and  Rhyolites  from  successive  flows  of 
igneous  matter  from  the  interior  of  the  Earth. 

Nevada  was  the  scene  of  great  eruptions.  As  many  as 
fifteen  distinct  flows  of  Rhyolite  have  been  noted  and  classi- 
fied by  the  United  States  Geological  Survey.  Andesite  in- 
trusions are  also  of  this  period,  all  of  which,  associated  with 
the  older  rock  formation,  tell  a  story  of  volcanic  activity 
without  a  parallel  in  the  earth's  history. 

The  igneous  formations  of  Cripple  Creek,  Colorado, 
Clifton  and  Bisbee,  Arizona,  belong  to  the  Tertiary  eruptions. 
They  are  generally  remarkable  as  ore  producers. 

What  Changes  Occurred  in  the  Quarternary  Period? 

41.  The  close  of  the  Tertiary  Period  saw  the  Earth  to 
all  appearance  ready  for  man,  but  the  whole  upward  process 
was  now  reversed.  The  long  tropical  summer  was  followed 
by  a  dismal  winter  that  geologists  believe  lasted  for  thous- 
ands of  years.  This  period  has  been  previously  described 
under  Glacial  Age,  and  was  probably  due  to  an  uplift  of  the 
Arctic  crust  causing  the  Polar  icebergs  to  drift  southward 
and  cover  the  North  American  Continent  east  of  the  Rockies. 

The  one  distinctive  crust  change  in  this  period  was  the 
grinding  and  polishing  of  the  surface  rocks  into  pebbles  and 


GEOLOGY  57 

boulders,  the  forming  of  a  successive  line  of  terraced  beaches 
and  the  filling  of  low  basins  with  silt  alluvium,  clay,  etc.,  to 
form  a  garden  spot  for  man. 

The  fossil  bones  of  primitive  man  and  his  rude  stone 
implements  are  conclusive  evidence  that  when  the  Glacial 
drift  receded,  man  came  upon  the  scene.  This  accords  with 
the  Mosaic  account  of  man's  creation  on  the  sixth  day  or 
period,  so  that  Geologic  and  Sacred  History  do  not  conflict  in 
the  "Days  of  Creation." 

What  Practical  Mining  Lessons  do  the  Geologic  Ages 
Teach  Us? 

42.  Two   things  stand  out  clearly  as  a   result  of  our 
tracing  the  changes  that  have  taken  place  in  the  Earth's  crust : 

(1)  The  Sedimentary,  or  water  formed  rocks,  do  not 
contain  metallic  minerals  of  use  to  man  in  sufficient  quantities 
to  be  extracted  with  profit.     It  is  true  that  gold  is  found  in 
placer  beds  where  nature  has  concentrated  it  from  the  mass  of 
detritus   washed   down   from   the   heights,   but   the   regular 
sedimentary  rocks  such  as  sandstone  may  usually  be  regarded 
as  "barren"  and  the  practical  miner  may  well  ignore  water- 
formed  rocks  in  mining  explorations. 

(2)  The  Igneous   (Fire)   and  Metamorphic   (Altered) 
Rocks  only  are  associated  with  metal  mineral  deposits,  the 
reason  for  which  may  not  as  yet  be  clear,  but  this  will  be 
fully  explained  under  the  subject  "Ore  Deposits." 

What  are  the  Three  Zones  in  the  Earth's  Crust? 

43.  We  have  traced   the  earth's  history  by  strata  and 
fossils  from  the  beginning  down  to  the  present,  and  it  now 
remains  to  consider  the  crust  with  reference  to  its  physical 


58      PRACTICAL  GEOLOGY  AND  MINERALOGY 

and  chemical  condition,  as  a  result  of  the  Geologic  changes 
due  to  heat,  moisture  and  gases. 

It  has  been  proven  that  the  Earth's  interior  is  intensely 
hot,  increasing  from  the  surface  downward,  and  this  fact 
taken  in  connection  with  the  action  of  water,  gases  and 
pressure,  produces  fairly  well  defined  crust-belts  which  are 
known  as  zones. 

The  principles  involved  in  these  changes  cannot  be  con- 
sidered here,  and  only  a  general  statement  as  to  the  existence 
and  condition  of  these  Zones  will  be  attempted  at  this  time. 

Surface  rocks,  being  formed  from  sediments,  are  more 
open  and  porous  than  the  deep-seated  rocks  of  the  same,  or 
different  materials.  The  weight  of  the  mass  above  compresses 
them  and  forces  out  the  air  and  water  from  the  open  spaces, 
making  a  close-grained  rock.  Such  rocks  filling  deep  depres- 
sions, tend  to  produce  a  solid  crust  which  the  eruptive  forces 
do  not  fracture  easily.  The  elevated  regions,  having  been 
pushed  up  from  below,  through  the  weaker  portion  of  the 
crust,  are  necessarily  more  fractured  and  broken  up  than 
elsewhere.  This  condition  favors  the  formation  of  mineral 
veins  and  ore  deposits,  and  it  is  to  such  sections  of  the  crust 
that  the  term  zone  more  particularly  applies. 

The  Three  Zones 

These  belts  are  known  under  the  following  names,  viz : 

( 1 )  OXIDE,  or  Fracture  Zone. 

(2)  SULPHIDE,  or  Fracture  and  Flo  wage  Zone. 

(3)  MOLTEN,  or  Flowage  Zone. 

(See  Illustrations,  Part  IV,  Fig.  47.) 

What  Characterizes  the  Oxide  or  Fracture  Zone? 

44.  This  zone  is  also  called  the  Weathering  zone,  because 


GEOLOGY  59 

of  the  influence  of  atmospheric  agencies  on  the  exposed  rocks. 

It  begins  at  the  surface  and  extends  downward  to  the 
permanent  water  level,  which  varies  in  dftierent  localities 
from  a  few  feet  to  the  depth  of  a  mile.  In  the  Oxide  zone 
the  rocks  are  under  moderate  pressure  from  above  and  when 
forced  to  move  by  internal  convulsions,  they  break  easily, 
causing  cracks  or  fissures  in  many  directions.  Owing  to  these 
fractures  it  is  usually  impossible  to  quarry  rocks  of  any  size 
for  building  purposes.  Often  rocks  that  appear  sound,  when 
handled  or  subjected  to  pressure,  show  their  hidden  defects. 
This  broken  up  condition  results  in  many  cavities  or  open 
spaces,  into  which  the  gases  of  the  atmosphere  and  the  water 
from  rains  and  melted  snows  find  their  way,  resulting  in  a 
process  called  oxidizing,  or  weathering.  The  general  effect 
of  this  process  is  to  disintegrate  the  parts  of  the  rocks  exposed 
and  carry  their  heavier  particles  into  larger  cavities  or  veins, 
rendering  the  rocks  still  more  open  and  porous. 

What  Distinguishes  the  Sulphide  or  Fracture  and 
Flowage  Zone? 

45.  This  Belt  has  a  distinct  line  separating  it  from  the 
Oxide  Zone,  in  the  permanent  water  level,  from  which  it 
extends  downward  to  the  depth  of  about  four  miles.  This  is 
also  called  the  Zone  of  Cementation,  because  the  cracks  or 
fissures  due  to  Earth  movements  have  a  tendency  to  cement 
together  much  as  a  crack  in  the  human  skin  heals  over  by 
natural  processes.  The  .cementing  material  is  furnished  by 
the  disintegrated  rocks  from  the  Zone  above. 

In  this  Zone  the  open  spaces  and  cavities  are  relatively 
small  decreasing  in  size  with  depth.  The  rocks  of  this  Zone 
are  continuously  being  fractured  by  the  eruptive  forces,  but  by 
the  pressure  of  the  mass  above  and  the  circulation  of  warm 


60      PRACTICAL  GEOLOGY  AND  MINERALOGY 

waters  charged  with  sedimentary  material  from  the  Oxidized 
rocks  above,  such  fractures  are  rapidly  repaired  and  cemented 
together  again. 

In  the  Sulphide  Zone,  the  more  rigid  rocks  like  quartz- 
site  may  fracture,  but  weaker  rocks  like  clay  bend  and  fold 
over  like  wax,  causing  all  cracks  and  cavities  to  rapidly 
disappear. 

What  Do  We  Know  About  the  Molten  or 
Flowage  Zone? 

46.  There  is  no  distinct  line  separating  the  Flowage  from 
the  Sulphide  zone,  as  they  blend  readily  into  each  other.  No 
shaft  has  ever  penetrated  the  Flowage  Zone,  hence  its  exist- 
ence is  largely  theoretical.  From  the  known  increase  in  tem- 
perature with  depth,  we  are  reasonably  certain  that  a  point 
would  be  reached  in  which  the  plastic  or  molten  state  due  to 
internal  heat,  taken  in  connection  with  the  great  pressure 
from  the  mass  above,  would  make  fractures  improbable  and 
only  hair-like  openings  could  exist. 

The  existence  of  the  Flowage  Zone  is  generally  recognized 
by  Scientists.  It  is  believed  to  begin  immediately  under  the 
Sulphide  Zone,  and  extend  downward  from  three  to  six  miles. 

Such  a  molten  mass  would  rapidly  change  form  like  wax. 
The  great  heat  would  prevent  any  surface  waters  from  re- 
maining in  this  Zone,  and  if  they  did  descend  to  this  depth, 
would  immediately  be  changed  into  vapor  and  rise  to  a  cooler 
Zone. 

The  conditions  in  this  Zone  are  favorable  to  the  formation 
of  heavy  silicates,  quartz,  feldspar,  serpentine,  etc.,  from  the 
disintegrated  primary  rocks. 

The  heat  in  this  Zone  is  doubtless  sufficient  to  change 
many  metals  to  a  gaseous  state,  and  these  metallic  vapors 


GEOLOGY  61 

arising  are  deposited  in  the  gangue  matter  of  previously 
formed  veins,  which  process  is  more  fully  explained  under 
"Ore  Deposits." 

Below  the  Molten  or  Flowage  Zone,  the  materials  are 
believed  to  be  in  that  fused  condition,  to  form  the  Igneous 
rocks  we  find  spread  out  on  the  surface  today.  All  metallic 
substances,  there  existing,  would  possibly  Volatilize  and  find 
their  way  upward  through  fissures,  filling  and  mineralizing 
existing  veins. 

How  to  Use  Geological  Survey  Maps  and  Reports 

47.  The  United  States  Government  recognizes  the  value 
of  Geological  information  to  the  miner,  and  it  is  for  his 
benefit  largely  that  this  valuable  department  is  maintained. 

A  Geologic  and  Topographic  Atlas  was  authorized  by 
law  in  1882,  and  about  half  of  the  United  States,  including 
Alaska,  has  already  been  mapped. 

These  maps  are  arranged  in  what  are  called  Quadrangles 
bounded  by  certain  meridians  and  parallels,  and  designated 
by  the  name  of  the  principal  town  or  prominent  natural 
feature  within  the  quadrangle.  About  1800  of  these  sheets 
have  been  engraved  and  printed,  and  they  may  be  obtained  at 
a  price  of  25c  each. 

No  mining  man  should  be  without  a  Geological  Map  of 
the  district  in  which  he  is  interested. 

In  addition  to  these  maps,  the  Department  issues  bulletins 
on  mineral  resources,  and  special  Annual  Reports  on  various 
subjects  of  interest  to  the  mining  man.  Many  of  these 
Department  papers  may  be  had  simply  for  the  asking,  and 
the  author  advises  every  reader  to  write  to  the  U.  S.  Geolog- 
ical Survey  Director,  Washington,  D.  C.,  for  a  list  of  the 


62       PRACTICAL  GEOLOGY  AND  MINERALOGY 

various  publications,   from  which  such  may  be  selected  as 
will  be  of  special  interest  to  you. 

Many  States  and  several  foreign  countries  now  maintain 
Departments  for  collecting  and  disseminating  information 
in  the  interest  of  the  mining  industry  and  such  documents 
may  be  had  by  applying  to  the  proper  authorities. 

The  United  States  Government  has  recently  recognized 
the  importance  of  a  knowledge  of  Geology  to  the  mining  man 
by  appointing  the  Director  of  Geological  Survey  to  the  head 
of  the  new  Department  of  Mines. 

The  Government  is  anxious  to  serve  you,  and  you  owe 
it  to  yourself  to  take  advantage  of  everything  so  freely 
offered. 


PART  II 

PETROLOGY 


Part  II 

PETROLOGY 


We  have  heretofore  treated  Rock  as  a  general  mass, 
forming  a  part  of  the  Earth's  crust,  but  we  shall  now  con- 
sider Rock  as  a  specific  material,  belonging  to  certain  classes 
or  groups,  each  having  its  own  peculiar  composition  and 
structure. 

What  is  Rock? 

1.  The  term  Rock  as  used  by  the  Geologist,  includes 
not  only,  the  stony  matter  familiarly  known  as  Rock,  but 
also  all  massive  mineral  substances  which  go  to  make  up  the 
Earth's  crust. 

This  would  include  sand,  pebbles,  clay  and  soil,  as  well 
as  the  same  materials  consolidated  into  hard  stones. 
The  terms  Rock  and  Stone  are  generally  used  to  mean  the 
same  thing,  but  a  strict  use  of  the  word  Stone  implies  a  rock 
that  has  been  shaped  or  cut,  as  a  precious  stone  or  building 
stone. 

What   is  Petrology? 

2.  The  word  Petrology  as  used  by  later  Scientists  is 
derived  from  the  Latin  Petra,  meaning  Rock,  and  Logos, 
study,  so  the  word  means  literally  rock-study  or  rock-science. 


66      PRACTICAL  GEOLOGY  AND  MINERALOGY 

Of  What  are  Rocks  Composed? 

3.  Rocks  may  be  classed  according  to  their  composition 
as  follows: 

(1)  Silica. 

(2)  Alumina. 

(3)  Lime. 

(4)  Silicates. 

The  last  named  has  silica  as  its  principal  constituent,  and 
the  Alumina  Rocks  are  also  forms  of  silica,  so  we  may  reduce 
all  rock  masses  down  to  two  general  classes,  called  Calcar- 
eous and  Silicious  Rocks. 

What  are  Calcareous   Rocks? 

Fig.  13  4.  The  word  Calcareous  is  from  the 

Latin  Calx  (lime)  and  the  adjective 
ending  ous  means  composed  of,  so  that 
a  Calcareous  Rock  is  principally  com- 
posed of  lime,  though  most  all  such 
rocks  contain  some  silicious  matter. 

Calcareous  cry*-  1-11 

tals.  1  he  common  calcareous  rocks  include 

chalk,  lime-spar  and  marble,  and  they  are  called  Carbonates 
because  of  the  Carbonic  acid  they  contain,  which  serves  to 
distinguish  them.  When  calcareous  rocks  are  burned  in  a 
Kiln,  the  acid  is  expelled  and  leaves  pure  lime,  called  Oxide 
of  Calcium.  (See  Fig.  15).  When  any  of  the  common  acids 
are  placed  on  Calcareous  stones,  they  fiz  or  effervesce,  like 
soda-water,  due  to  the  escaping  carbonic  acid  gas.  Even 
vinegar,  which  is  a  fruit  acid  diluted  with  a  large  percentage 
of  water,  when  placed  on  a  lime  rock,  will  cause  it  to  fiz. 
Lime  rocks  are  nearly  all  soft  and  can  be  scratched  with  a 
nail  or  knife  and  this  fact  serves  to  further  identify  them. 


PETROLOGY 


67 


What  is  the  Origin  of  Calcareous  Rocks? 

5.  If  we  examine  a  piece  of  chalk  with  a  good  micro- 
scope, we  find  it  composed  of  minute  shells,  which  proves 
that  chalk  is  simply  a  consolidation  of  animal  fossils. 
Animals  have  the  power  of  secreting  lime  from  the  water  in 
which  they  live.  Even  when  lime  rock  contains  no  visible 
fossils,  it  is  possible  that  the  sea  has  ground  the  shells  and 


Fig.  15 


Fig.  16 


Lime-kiln.    When     ilca- 

rfous   stones   are    subjected  to  a 

very  high  temperature   they  are 

transformed  into  lime.  An  oven  for  burning  plas- 

ter. Gypsum  subjected  to  a  great 
heat  becomes  plaster. 

corals  into  fine  powder  which  settles  out  forming  sedimentary 
lime  rocks.  When  such  lime  sediments  are  brought  under 
the  influence  of  heat  and  pressure  within  the  earth,  they 
crystallize  into  Calcite  (calc-spar)  and  marble,  which  action 
destroys  the  original  fossil  shapes. 

We  have  seen  that  in  the  Cretaceous  Age,  vast  strata 
were  formed  so  that  it  was  known  as  the  Chalk  Period. 
From  the  vast  amount  of  lime  rock  in  the  world  today  an 
idea  may  be  formed  of  the  animal  life  that  must  have  existed 
in  past  ages. 


68      PRACTICAL  GEOLOGY  AND  MINERALOGY 

How  Do  Limestone  and  Dolomite  Differ? 

6.  Magnesian     Limestone    is    called     Dolomite.      The 
magnesia  in  it  makes  it  harder  than  Limestone  and  it  will  not 
effervesce  in  ordinary  acids,  unless  heat  is  applied,  and  these 
two  facts  make  it  comparatively  easy  to  distinguish  between 
Limestone  and  Dolomite. 

What  is  the  Composition  of  Marble? 

7.  Marble  is  crystallized  limestone  and  its  origin  is  due 
to  the  solution  or  the  fusion  of  limestone,  which  in  cooling  and 
precipitating  forms  into  a  crystalline  structure.    When  clear- 
marble  is  broken,  the  fine  grains  or  crystals  show  like  loaf 
sugar.    The  various  colors  of  marble  are  given  it  by  iron  and 
other  impurities.    Ordinary  fruit  acids  like  vinegar  or  lemon 
juice  affect  marble,  while  the  stronger  acids  cause  it  to  effer- 
vesce.    The  acids    of    the    atmosphere  slowly    decompose 
marble,  so  while  very  pretty,  marble  will  not  endure  like 
granite  or  sandstone. 

What  is  Gypsum? 

8.  This  is  also  a  Calcareous  rock,  but  it  contains  sulphur 
chemically  combined,  hence  is  called  Sulphate  of  Lime. 

Gypsum  is  only  slightly  affected  by  acids,  owing  to  the 
sulphur  content.  It  is  softer  than  Calcite,  and  these  two 
points  will  usually  serve  to  distinguish  Gypsum  from  ordin- 
ary Lime  rock.  (See  Fig.  14). 

There  are  two  forms  of  Gypsum:  That  crystallized  in 
fibrous  masses  of  pearly  luster  is  called  Satin-Spar;  when  it 
appears  in  scale  layers  and  crystals,  it  is  called  Selenite,  which 
if  snowy  white  and  solid  is  called  Alabaster.  When  Gypsum 
is  burned  the  sulphur  is  driven  off,  leaving  what  is  known 
as  Plaster  of  Paris.  (See  Fig.  16.) 


PETROLOGY 


69 


The  Uncrystallized  Gypsum,  ground  into  white  powder, 
is  sold  as  plaster  for  fertilizer,  also  used  in  the  manufacture 
of  Portland  Cement. 

What  are  Silicious  Stones? 

9.  The  word  Silicious  means  composed  of  Silica,  but 
do  not  understand  they  are  composed  wholly  of  silica.  As  a 

Fig.  17 


A  Cluster  of  Quartz  Crystals  from  Lake  Superior. 

matter  of  fact  many  silicious  stones  contain  some  calcareous 
matter.  A  familiar  example  of  Silica  is  quartz,  which  is 
called  an  oxide  of  silicon  made  up  of  Oxygen, — a  gas,  and 
silicon — a  solid.  Quartz  is  so  hard  that  it  strikes  fire  with 


70      PRACTICAL  GEOLOGY  AND  MINERALOGY 

steel  and  will  scratch  glass,  but  cannot  be  scratched  with  a 
knife.  It  breaks  into  irregular  fragments  which  have  a 
glassy  luster.  Quartz  is  generally  a  fire-formed  rock,  and  in 
cooling  it  arranges  into  crystals,  sometimes  very  large,  but 
many  quartz  crystals  require  a  magnifying  glass  to  make 
them  plain  to  the  ordinary  observer.  ( See  Fig.  17). 

The  Silicious  stones  are  the  most  plentiful  form  of  rock 
and  make  up  more  than  half  the  Earth's  crust.  Flint  and 
pebbles  are  the  most  common  silicious  stones. 

Silica  is  insoluble,  that  is  it  cannot  be  dissolved  by  com- 
mon acids,  and  is  infusible  alone,  that  is,  cannot  be  melted 
except  by  using  a  flux. 

There  are  many  forms  of  quartz,  known  as  Pink,  Smoky, 
Milky,  Granular,  etc.  The  latter  when  powdered  is  used  for 
making  sand  paper,  glass  and  pottery.  Silica  when  powdered 
and  air-floated  is  used  as  a  body  for  paints,  used  at  first  as  an 
adulterant,  but  now  known  to  stand  the  weathering  action 
equal  to  lead  paints.  The  Amethyst,  Chalcedony,  Agate  and 
Jaspar  are  Precious  Stones  composed  almost  entirely  of 
Silica,  and  the  distinctive  colors  are  due  to  the  presence  of 
other  elements  as  impurities. 

What  is  the  Origin  of  Quartz? 

10.  As  already  stated,  quartz  is  a  compound  of  silica 
and  oxygen.  It  is  not  a  native  rock,  and  occurs  principally 
in  veins.  The  deepest  seated  rock  is  Granite,  which  is  nearly 
three-fourths  silica.  It  is  believed  that  the  heat  and  pressure 
of  the  Flowage  Zone  previously  described  separates  out  the 
silica  from  the  primitive  rocks  and  the  eruptive  forces  project 
it  upward,  through  fissures  into  the  Oxide  Zone,  where  it 
combines  with  the  oxygen  there  present,  forming  what  we 
know  as  quartz,  filling  veins  for  the  reception  of  metallic 


PETROLOGY 


71 


minerals.     Quartz  has  been  well  termed  the  "Mother  of 
Gold,"  since  it  forms  the  universal  matrix,  or  shell  covering 
P.     .g  gold.     However,  Quartz  is  not 

always  mineralized,  but  often 
occurs  in  dykes,  in  the  older  for- 
mations, perfectly  "barren"  of 
any  metals,  sometimes  called 
"Bull  Quartz." 

Quartz  is  also  found  in  many 
places  where  ledges  and  veins 
do  not  appear,  so  it  would  ap- 
pear that  there  is  another  source 
of  origin. 

It  is  quite  probable  that  most 
of  the  Flint  and  Horn-stone  is 
of  animal  or  vegetable  origin. 
Sponges  are  known  to  secrete 
.ittle  points  of  silica  from  the 
muddy  sea  bottom. 

DIATOMS  are  little  one-celled 
organisms,  too  small  to  be  seen  with  the  naked  eye,  yet  when 
gathered  into  countless  myriads  they  appear  as  a  silicious 
slime.  They  have  the  power  to  separate  the  silica  from  the 
sediment,  and  when  these  diatoms  die  their  silicious  frame- 
work form  strata  of  great  extent  and  thickness.  This  is 
also  the  origin  of  what  is  called  Tripoli  and  Infusorial 
Earth,  and  the  proof  of  this  is  that  Flint  and  Hornstone, 
under  powerful  microscope,  usually  show  fossils  of  these 
animal  and  vegetable  organisms.  (See  Fig.  18). 

What  are  Silicates? 

1 1 .     These  are  compounds  of  Silica  and  other  elements, 
as  alumina,  lime,  magnesia,  potash,  and  iron  oxides. 


Diatoms  from  Albany  and  Waterfcrd» 

Maine. 

B  is  magnified  25  Diameters. 
C  is  magnified  250  Diameters'. 
D  is  magnified  200  Diameters, 


72       PRACTICAL  GEOLOGY  AND  MINERALOGY 

FELDSPAR.  This  is  somewhat  softer  than  quartz  and 
breaks  in  two  directions,  leaving  a  pearly 
flat  crystal  surface,  and  these  characteris- 
tics will  generally  enable  any  one  to  dis- 
tinguish Feldspar  from  Quartz. 

Feldspar   decomposes   easily   and   when 
mixed  with  pulverized  silica  forms  common 
clay.    Pure  feldspar  sediment  forms  Kaolin, 
from  which  porcelain  is  made.     (See  Fig.  19.) 

MICA  (Micare — to  Glisten).  Isinglass  is  a  common 
name  for  mica.  When  in  large  sheets  it  is  used  for  windows 
in  stoves.  Small  flakes  of  mica  in  rock  may  be  mistaken  by 
the  novice  for  gold,  but  mica  glistens,  can  be  broken  easily 
into  scales,  or  picked  out  with  the  point  of  a  pen-knife,  and 
it  is  often  so  light  as  to  float,  so  that  no  one  should  ever 
mistake  mica  for  gold. 

Hornblende,  Pyroxine,  Serpentine,  Talc  and  Chlorite 
are  silicates,  carrying  Magnesia,  Lime  and  Alumina  in 
varying  proportions. 

How  are  Rocks  Classified? 

12.  In  our  examination  of  the  Earth's  crust  we  found 
two  kinds  of  rocks,  with  reference  to  their  origin  one  formed 
by  fire,  known  as  Igneous  Rock,  the  other  formed  by  water, 
known  as  Aqueous  Rock.  Fire  and  Water  are  two  opposing 
agencies,  hence  an  Aqueous  Rock  brought  into  contact  with 
the  heat  from  the  fiery  furnace  within  the  Earth,  undergoes 
a  change  so  that  it  partakes  of  the  nature  of  each,  and  is  then 
called  Metamorphic,  which  means  changed  or  altered  rock. 


PETROLOGY  73 


What  are  Aqueous  Rocks? 

13.  These  are  so  called  from  Aqua,  Latin  for  water, 
which   deposits  sediment   from   decomposed   rocks,    forming 
regular   layers,    and    hence    are   sometimes    called    stratified 
rocks. 

SANDSTONE  is  a  common  form  of  Aqueous  Rock,  and  is 
composed  mainly  of  sand,  pressed  and  dried  by  the  earth's 
heat,  so  that  when  deep  seated  forms  a  very  dense  rock. 

CONGLOMERATE  Stone  is  made  up  of  pebbles,  calcareous 
and  silicious  matter,  all  mixed  together  in  a  pasty  mass, 
which  is  cemented  together  much  as  concrete  in  a  pavement 
or  building.  Gold  and  precious  stones  are  sometimes  found 
in  a  Conglomerate  formation,  as  in  the  Rand  Mines  of  South 
Africa. 

SHALE  is  simply  clay,  dried  and  compressed  so  that  it 
splits  into  thin  flakes  or  laminae. 

SLATE  is  simply  shale  subjected  to  long  continued  pressure 
and  baked  by  internal  heat  of  the  Earth. 

What  are  Igneous  Rocks? 

14.  These  rocks  are  so  named  from  the  Latin,  I  gnus, 
meaning   fire,    and    hence    Igneous    Rocks    are    fire-formed. 
These    have    been    thrown    out    from    the    earth's    interior, 
through  openings,  while  highly  heated  or  in  a  molten  state. 
Igneous   rocks  are  not   arranged   in  layers,   and  hence  are 
sometimes  called  Unstratified  Rocks.     They  are  sometimes 
wavy  from  the  flowing  molten  mass.     The  Igneous  Rocks 
are  arranged  in  two  classes,  known  as — 

(1)  Trap  Rocks. 

(2)  Volcanic  Rokcs. 


74       PRACTICAL  GEOLOGY  AND  MINERALOGY 

What  are  Trap  Rocks? 

15.  The  word  Trapa  is  Swedish  and  means  stairs  or 
steps,  and  Trap  Rocks  are  often  found  arranged  like  stepping 
stones,  or  in  the  form  of  massive  terraces  or  bluffs.  Fig.  20 
shows  a  fragment  of  Basalt,  in  the  shape  of  a  six-sided 
column.  This  form  of  crystallization  is  common  to  Trap 
Rocks  everywhere.  The  Pictured  Rocks  of  Lake  Superior, 
the  Palisades  of  the  Hudson,  and  the  Giants  Causeway  in 
Ireland,  are  the  most  noted  examples  of  massive  Trap  Rocks. 
They  are  very  hard,  but  are  seldom  used  for  any  practical  pur- 
pose except  in  road  building.  The  principal  Trap  Rocks  are : 

(a)  Basalt. 

(b)  Diorite. 

(c)  Porphyry. 

(d)  Amygdaloid. 

20  (a)   BASALT.  This  is  called  Dolerite,  from 

Dolerous,   deceptive,   because  the  composition 
is  difficult  to  determine,  being  mainly  Feldspar 
and  Augite.    The  colors  are  various  but  most- 
^: "          ly    of    a    bottle    green,    having    small    crystal 


(b)  DIORITE.     This  is  also  called  Greenstone,  from  its 
color,  the  composition  being  principally  Feldspar  and  Horn- 
blende, the  latter  occurring  in  needle  pointed  crystals. 

(c)  PORPHYRY  (Purple).     This  rock  was  originally  so 
named   from  a  purple  variety  found  in  Egypt,  and   highly 
prized.     The  word  Porphyry  is  now  used  to  designate  any 
Igneous  rock  containing  Feldspar  crystals.     It  appears  to  be 
imperfectly  crystallized  lava  and  is  of  much  importance  to 
the  mining   man,   as   it   is  closely  associated   with   mineral 
veins,  and  ore  deposits,  though  not  usually  found  in  the  vein 
itself.     (See  Fig.  21.) 


PETROLOGY 


75 


(d)   AMYGDALOID  (Almond).     This  is  a  Trap  Rock 
containing  cavities,  often  filled  with  Calcite,  Quartz,   etc., 
so  that  a  weathered  surface  appears  like  a  cake  stuck  full  of 
almonds.     (See  Fig.  22.) 

The  general  form  of  all  Trap  Rocks  is  that  of  a  column 
or  prism  having  three  to  eight  sides  and  a  diameter  running 
from  a  few  inches  to  many  feet;  such  pillars  are  often  left 
standing  several  hundred  feet  high,  having  the  appearance 
of  an  old  castle  ruin. 


Fig.  21 


Fig.  22 


Porphyry. 


Lava  (Scoria),  in  part  turned  into  an 
Amygdaloid.' 


16. 

(a) 


What  are  the  Volcanic  Rocks? 

There  are  two  common  varieties  of  Volcanic  Rocks : 
Trachite. 


(b)    Lava. 

(a)  TRACHITE  (Trachus — rough).  This  is  so  named 
from  its  rough,  gritty  feel.  It  is  of  porous  open  structure 
and  light  weight,  and  has  various  colors  running  from  white 
to  gray  and  black.  The  cones  of  many  extinct  volcanoes  are 
formed  of  Trachite.  Rhyolite  is  a  trachite  with  quartz 


76      PRACTICAL  GEOLOGY  AND  MINERALOGY 

crystals,  and  has  many  different  colors,  but  generally  of 
rough  fracture  and  often  has  wavy  lines  from  flowing  while 
in  a  molten  condition. 

(b)  LAVA.     This  name  is  given  to   all  molten  matter 
flowing  from  Volcanoes.     When  lava  cools,  the  upper  por- 
tion of  the  stream  is  light  and  porous,  while  the  under  portion 
cooling  more  slowly  is  similar   to   Basalt.     Lava  contains 
Feldspar  and  Pyroxine  and  one  hundred  different  varieties 
have  been  observed  in  the  eruptions  of  Vesuvius. 

(c)  PUMICE  stone  is  Feldspathic  Scoria  from  Volcanoes: 
it  is  porous  and  has  slender  air-cavities,  so  that  it  is  some- 
times found  floating  in  the  ocean. 

(d)  OBSIDIAN  is  volcanic  glass  that  has  separated  out 
from  Lava. 

What  are  the  Metamorphic  Rocks? 

17.  We  have  seen  how  an  Igneous  rock  may  be  disin- 
tegrated and  washed  down  to  a  basin  to  become  an  aqueous 
rock.  This  is  a  complete  change.  When  a  sedimentary  rock 
comes  in  contact  with  the  intense  heat  of  the  earth's  interior, 
it  suffers  a  change,  so  that  it  partakes  of  the  nature  of  both  an 
igneous  and  aqueous  rock,  and  it  is  then  called  a  Metamor- 
phic rock.  The  word  Metamorphic  means  altered  or 
changed,  and  the  principal  agencies  causing  the  change  are 
heat,  pressure  and  moisture. 

For  example, — Lava  penetrating  an  aqueous  rock  would 
alter  its  character,  the  clay  be  changed  into  slate,  the  lime- 
stone altered  into  marble,  and  earth  rock  like  sandstone 
be  transformed  into  quartzsite  or  even  granite.  In  this 
Metamorphic  process,  the  stratification  would  be  destroyed 
and  the  fossils  partially  or  entirely  obliterated.  A  metamor- 


PETROLOGY  77 


phic  rock  examined  under  a  microscope  will  sometimes  show 
a  fossil,  spangles  of  metal  or  mica.  Often  little  nodules  or 
lumps  of  ironstone  enclose  imperfectly  formed  quartz  crys- 
tals, or  garnets  may  be  sprinkled  throughout  the  mass. 

There  are  a  vast  number  of  these  Metamorphic  Rocks, 
but  space  forbids  more  than  a  mention  of  a  few  prominent 
types. 

Granite,  What  It  is  and  How  Formed. 

18.  We  have  seen  that  Granite  is  an  Azoic  Rock,  lying 
at  the  bottom  of  all  formations,  yet  we  find  it  capping  the 
highest  mountains. 

P.  As   a   primitive   rock,   Granite   is 

hard  and  compact,  but  as  a  Metamor- 
phic rock,  its  most  abundant  form,  it 
is  more  or  less  fractured  so  that  it  is 
often  as  easily  crushed  and  weathered 
as  Limestone.  (See  Fig.  23.) 

The   word    is    from    Granum,    a 
a  mixture™? quart£?eC£  grain,  and  indicates  its  granular  struc- 
ture.    The  composition  of  granite  is 

Quartz,  Feldspar  and  Mica.  Metamorphic  Granite  occurs 
in  veins,  hills  and  masses  which  were  forced  up  through  the 
crust  in  a  moist,  pasty  condition  and  crystallized  from  con- 
tact with  the  cool  atmosphere.  Granite  is  always  newer  or 
younger  than  the  rocks  it  fissures,  or  through  which  it  has 
been  ejected.  The  fact  that  Granite  is  composed  of  nearly 
the  same  elements  as  sandstone  and  clay  has  led  some  to 
conclude  that  most  granite  has  been  formed  by  a  Metamor- 
phosis of  the  sedimentary  rocks.  Granite  Peaks  always 
appear  single  in  well  rounded  summits,  while  volcanic  rocks 
like  Basalt  always  appear  as  twin  mountains  with  tops 
flattened  into  cones.  (See  Fig.  24.) 


78      PRACTICAL  GEOLOGY  AND  MINERALOGY 

GNEISS  (Nice)  differs  from  Granite  only  in  being  ar- 
ranged in  layers  from  pressure  and  points  to  the  same  origin. 

MICA  SCHIST  is  a  leaf-like  arrangement  of  quartz  and 
mica,  the  latter  probably  derived  from  a  decomposition  of 
Feldspar. 

SYENITE.  This  is  a  Granite  in  which  the  Mica  is 
replaced  by  Hornblende.  It  possesses  great  strength  and 
withstands  enormous  pressure.  It  is  generally  grayish  in 
color  due  to  its  chief  constituents,  Feldspar  and  Hornblende. 

Fig.  24 


Volcanic  Cones,  near  Mono  Lake. 

TALCOSE   SCHIST  is  a  slate   that  contains  much  Talc. 

CHLORITE-SCHIST  contains  the  olive-green  mineral 
Chlorite  (resembling  Talc)  together  with  slate  and  clayey 
shale.  It  is  usually  associated  with  gneiss. 

How  Do  Rocks  Differ  in  Structure? 

19.     With  reference  to  the  structure,  rocks  are  either: — 


PETROLOGY 


79 


( 1 )  Stratified  Rocks. 

(2)  Unstratified  Rocks. 

. .  STRATIFIED  ROCKS.  When  the  earth's  crust  was  lifted 
up  and  dry  land  was  formed,  it  began  to  erode  under  the 
ceaseless  action  of  rains,  winds  and  water,  the  debris  being 
carried  down  to  the  basins  where  it  was  deposited  in  flat 
layers  as  shown  in  Fig.  25.  If  it  had  not  been  for  eruptions 

Fig.  25 


of  igneous  rocks  and  uplifts  of  the  crust,  these  rock  strata 
would  have  remained  just  as  formed  and  it  would  have  been 
impossible  for  us  to  read  the  earth's  history  as  we  now  do, 
by  strata  and  fossils.  The  rocks  of  the  crust  have  not  been 
penetrated  by  man  more  than  a  mile  in  depth  in  a  perpendic- 
ular line,  but  fortunately  we  are  able  to  examine  the  stratified 
rocks  without  descending  into  the  earth,  by  reason  of  their 

Ftg.  26 


being  tilted  up  on  the  edges.  If  we  follow  a  deep  chasm  like 
the  Grand  Canyon  of  Arizona  which  is  about  a  mile  deep, 
the  successive  strata  and  formations  are  easily  observed.  So 
in  following  a  river  course  in  mountain  regions,  where  there 
are  numerous  waterfalls,  the  rocks  representing  the  successive 
ages  previously  described  may  be  plainly  observed,  the  older 


80      PRACTICAL  GEOLOGY  AND  MINERALOGY 

strata  below  and  the  younger  at  the  higher  points,  as  seen  in 
Fig.  26.  The  layers  that  have  been  exposed  by  the  action  of 
running  water  are  called  the  "Outcrop."  Where  the  forma- 
tions have  simply  been  tilted  up,  the  exposed  edges,  originally 
formed  one  uplifted  wall  of  a  fissure,  while  the  other  wall 
may  have  remained  stationary,  or  even  sunken. 


Fig  27 


A  curious  result  of  changes  in  stratified  rocks  by  the 
intrusion  of  Igneous  rocks  from  below  is  seen  in  Fig.  27. 
The  dark  strata  lines  in  the  different  sections  were  originally 
flat  as  in  Fig.  25. 

You  will  notice  the  igneous  rocks   forced   through   and 


Fig.  28 


overlying  the  stratified  rocks  at  the  highest  points.  This 
illustrates  the  origin  of  hills  and  mountains,  the  sections  of 
stratified  rocks  remain  more  dense  and  compact,  while  the 
igneous  intrusions  are  more  open  and  porous,  serving  as 
chimneys  and  funnels  to  let  out  the  heat  and  vapors  of  the 
furnace  beneath  and  making  conditions  favorable  for  the 
formation  and  the  filling  of  mineral  veins. 


PETROLOGY  81 


What  are  Strata,  Formations  and  Groups? 

20.  One  or  more  layers  of  Sedimentary  rock  are  called 
a  STRATA.  Several  strata  of  such  rock,  deposited  during  the 
same  period  as  shown  in  Geological  Section  (page  48),  make 
what  is  known  as  a  FORMATION.  When  formations  and  the 
strata  included  are  similar,  they  are  called  GROUPS. 

Strata  are  said  to  be  Horizontal  when  laid  down  by 
water-level  as  at  A  in  Fig.  28.  At  B  the  strata  is  said  to  be 
Inclined.  At  E  strata  is  said  to  be  Tilted  Up;  and  the  angle 
formed  is  called  the  "Dip";  C  is  Vertical  and  D  Contorted 
(Twisted).  An  Anticlinal  is  formed  by  strata  looped  at  the 
upper  end,  the  lower  end  of  loop  or  trough  is  called  a  Sincline, 
as  shown  in  Fig.  29 ;  where  strata  are  cut  through  by  water 
it  is  called  an  Escarpment,  or  Bluff  as  at  E.  When  strata 
are  arranged  one  above  the  other  as  at  O  they  are  said  to  be 
Conformable. 

In  Fig.  30  is  shown  strata  said  to  be  Uncomformable, 
the  uplifting  and  faulting  of  the  older  strata  was  followed  by 
a  period  of  "weathering"  which  wore  off  the  tilted  edges. 
Later  the  strata  sank  and  was  covered  by  water,  which  de- 
posited sedimentary  matter  in  horizontal  layers,  as  seen  in 
upper  portion  of  Fig.  30.  An  Ideal  Section  of  true  Uncon- 
formity is  seen  in  Fig.  31.-  The  ancient  strata  were  uplifted 
while  in  a  plastic  state,  forming  bends  and  folds;  the  crust 
was  later  submerged  under  the  seas,  the  Anticlinals  were 
worn  off  and  new  stratified  rocks  laid  down  as  shown  in  the 
upper  part  of  the  Figure  leaving  the  older  rocks  unchanged, 
and  making  what  is  sometimes  called  Diverse  Stratification. 


.8? 
U, 


§  §£ 


IJ 


PETROLOGY 


What  are  Folds? 


Fig.  32. 


A  Decapitated  Fold 


21.  When  rocks  are  young 
and  somewhat  plastic  the 
eruptive  forces  within  the 
earth  produce  elevations  and 
depressions  in  wave-like  ar- 
rangement, instead  of  produc- 
ing cracks  and  fissures.  (See 
Figs.  28  and  29.)  Rocks  folded  in  this  manner  have  their 
upper  folds  (anticlines)  worn  off  by  erosion  and  the  strata 
then  appear  standing  on  edge  and  parallel  to  each  other,  as 
shown  in  Fig.  32.  To  the  left  is  shown  a  Fold,  and  at  the 
right  is  the  same  after  it  has  been  eroded.  B  is  the  lower  or 
older  strata  in  the  fold,  but  after  erosion  B  appears  under  A, 
and  gives  the  appearance  of  being  older,  because  the  condi- 
tions appear  reversed.  This  sometimes  occurs  in  veins,  and 
the  inexperienced  miner  will  often  conclude  that  there  are 
two  parallel  veins  when  the  two  parts  are  simply  an  anti- 
clinal worn  off  by  erosion,  and  really  one  vein. 

Fig.  29 


What  are  Faults? 

22.  Cracks  and  fissure  in  rocks  are  very  common. 
They  are  called  Faults,  because  they  are  imperfections, — that 
is,  unnatural.  After  stratified  rocks  become  firm  and  rigid 
by  compression  and  heating,  they  no  longer  bend  and  fold, 
but  crack  and  break  across  the  grain  by  unequal  strain  from 
beneath.  One  side  of  the  strata  may  be  forced  upward,  the 


84      PRACTICAL  GEOLOGY  AND  MINERALOGY 

other  wall  may  remain  stationary  or  slip  downward.  This 
produces  what  are  called  dislocations,  somewhat  like  a  joint 
out  of  place  in  the  human  body.  A  series  of  Faults  or  off- 
sets are  shown  in  Fig.  33  shown  at  a,  b,  c  and  d.  These 

Fig.  33 


Faults  Qottets)  in  Mt.  Pleasant  Iron  Mine,  Rockaway,  N.  J. 
Faults  are  seldom  perpendicular,  but  the  Faults  are  frequent- 
ly parallel  and  the  structure  is  said  to  be  Jointed. 

What  are  the  Unstratified  Rocks? 

23.  The  Unstratified  Rocks  are  found  as  shapeless 
masses  underlying,  overlying  and  sometimes  penetrating  the 
sedimentary  rocks.  The  Stratified  rocks  record  the  Earth's 
formation  period,  while  the  unstratified  rocks  record  the 
Earth's  convulsions. 

The  Stratified  Rocks  are  water-formed,  while  the  Un- 
stratified Rocks  are  fire-formed.  Molten  matter  is  liquid, 
and  when  a  liquid  cools  and  becomes  a  solid,  like  elements 
are  attracted  so  that  they  separate  out  and  form  into  crystals. 
It  is  thus  that  the  Unstratified  Rocks  are  formed,  and  hence 
they  are  also  known  as  Crystalline  Rocks. 


PETROLOGY  85 


The  six  kinds  of  Crystals  in  minerals  have  been  noted 
and  classified,  which  are  fully  explained  under  Mineralogy. 
The  natural  position  of  crystalline  rocks  is  in  the  Earth's  in- 
terior, in  the  Fracture  and  Flowage  Zones,  inasmuch  as  their 
origin  is  due  to  the  fused  mass  below.  In  the  molten  state 
there  can  be  no  crystals  formed,  an  it  is  only  when  such  mat- 
ter is  forced  up  into  the  cooler  Zones  that  crystals  take  form. 
Crystals  are  also  formed  by  precipitation  (throw-down)  from 
liquids,  so  crystalline  rocks  may  be  the  result  of  both  these 
agencies. 

Fig.  34 


OB  A 

When  the  unstratified  rocks  are  forced  up  through  open- 
ing in  the  crust  they  often  fill  fissures  spread  out  and  overly 
the  surface  Sedimentary  Rocks. 

Fig.  34  illustrates  the  principles  named.  At  c  is  an 
underlying  Crystalline  rock;  e  is  a  stratum  forced  up  be- 
tween Sedimentary  rocks;  d  is  a  mass  pushed  up  through  a 
fissure  and  overlaps  the  Aqueous  rocks;  a  is  an  igneous  mass 
thrown  up  as  a  mountain  peak,  disrupting  the  regular  rocks 
and  leaving  them  tilted  up. 

What  are  Dikes  and  Veins? 

24.  We  have  seen  that  a  Fault  is  a  crack  in  the  rocks, 
and  a  later  movement  of  one  or  both  walls  displaces  the 
strata,  but  Faults  leave  no  permanent  openings.  When  a 


86      PRACTICAL  GEOLOGY  AND  MINERALOGY 

crack  remains  open,  gases  escape  through  it.  Later  move- 
ments increase  the  size  of  the  fissure,  while  the  eruptive 
forces  drive  igneous  matter  upward,  spreading  the  walls 
apart,  and  it  is  thus  that  Faults  become  fissures,  and  when 
filled  with  crystalline  matter  may  become  Veins. 

DIKES  are  fissures  filled  with  igneous  matter  pushed  up 
from  below.  Dikes  differ  from  Veins  in  being  formed  at 
one  eruption  of  a  uniform  igneous  mass,  while  Veins  usually 
have  several  kinds  of  filling,  the  result  of  a  number  of 
eruptions;  often  the  minerals  are  arranged  in  bands.  Dikes 
are  usually  larger  than  Veins  and  the  walls  are  more  nearly 
parallel,  and  seldom  branch  or  form  into  systems  like  Veins. 
The  word  Dike  means  a  wall ;  the  volcanic  filling  is  always 
harder  than  the  adjacent  rocks,  so  yields  slowly  to  weather- 
ing forces.  For  this  reason  Dikes  often  stand  out  promi- 
nently so  that  they  can  be  traced  easily.  In  Fig.  35,  c,  is  a 

Fig.  35 


b  e 

Fault  in  the  rocks  and  being  filled  with  igneous  rock,  be- 
comes a  Dike ;  at  a,  is  a  series  of  Veins  traversing  both  strati- 
fied and  unstratified  rocks. 

What  is  the  Origin  of  Veins  and  Dikes? 

25.  In  drying  and  cooling  the  crust  contracts  and  this 
shrinking  causes  cracks  or  openings  of  various  sizes.  As  in 
the  human  body  nature  collects  material  to  heal,  or  cement 
together  such  fractures.  Some  openings  are  filled  with 


PETROLOGY 


87 


igneous  matter  ejected  from  below,  which  cool  and  crystal- 
lize; we  know  this  by  the  burning  and  scouring  of  the  wall 
rocks  of  fissures  and  by  the  marks  (stria)  cut  into  the  wall 
rocks,  by  the  upward  movement.  In  many  instances  Dikes 
passing  through  strata  of  Lime  or  Chalk,  form  Marble. 
Some  fissures  are  filled  by  dissolved  matter  from  adjacent 
rocks,  which  process  is  more  fully  explained  under  subject 
"Ore  Deposits." 

When  Veins  or  Dikes  cross  or  fault  each  other,  as  is 
not  uncommon,  the  respective  ages  of  each  are  easily  told. 
The  older  is  always  cut  by  the  younger  or  newer  formation. 
This  principle  becomes  important  in  mineral  Veins,  as  the 
younger  veins  are  usually  a  less  important  source  of  minerals. 

Fig.  36 


Dike. 

at.   A  Quartz  Vein  passing  through  a  Greenstone 
Dike  and  Layers  of  Gneiss. 

In  Fig.  36,  we  have  a  Quartz  Vein(ab)  passing  through 
a  Greenstone  Dike.  Here  we  know  the  Quartz  Vein  is 
younger  than  the  Dike,  and  the  adjacent  rock,  because  it 
cuts  and  continues  through  each.  Had  the  Dike  been 
younger  or  later  formed,  it  would  cut  off  the  Quartz  Vein. 

Veins  are  not  confined  to  regular  fissures  in  rock  forma- 
tions. Large  rocks  wholly  disconnected  from  fissures  often 
have  seams  which  have  been  filled  by  matter  crystallized  out 


88      PRACTICAL  GEOLOGY  AND  MINERALOGY 

of  adjacent  rocks.  These  clefts  are  usually  mended  with  the 
strongest  materials  at  hand,  from  highly  heated  water 
charged  with  mineral  matter. 

Fig.  37 


Vein-form  Pebble  from  Drill,  Elrnira. 

Granite  eruptions  are  frequently  found  with  many  rocks 
filled  with  Quartz  or  Feldspar,  and  the  finest  seams  are  filled 
with  crystalline  matter,  deposited  originally  in  a  pasty  mater- 
ial, showing  nature's  process  of  repairing  rock  fractures. 
(See  Fig.  37.) 


PART  III 

MINERALOGY 


Part  III 

MINERALOGY 

Introduction 

1.  We  have  learned  that  the  Mineral  Kingdom    (see 
page  31)    includes  every  form  of  matter  not  Animal  nor 
Vegetable   and   that   when   life  » ceases   in   the   animal    and 
vegetable,   they   too   return   to   their  original   mineral   sub- 

.  We  have  also  seen  that  the  term  Rock  in  a  general 
sense  covers  every  form  of  mineral  matter,  having  no  refer- 
ence to  the  composition  or  proportion  of  the  combined  sub- 
stances, but  we  shall  now  regard  a  mineral  in  a  particular 
sense. 

What  is  a  Mineral? 

2.  A  MINERAL  is  a  distinct  kind  of  rock,  and  may  be 
either  a  single  substance,  as  Gold,  or  a  combination  of  sub- 
stances, as  Quartz,  which  is  made  up  of  two  elements,  Silicon 
and    Oxygen,    not    merely   mixed    together,    but    united    in 
certain  fixed  proportions  of  each  constituent. 

How  are  Minerals  Formed? 

3.  It  has  already  been  explained  that  Crystalline  Rocks 
are    formed    within    the    earth    largely    by    igneous    action. 
Minerals  are  the  highest  form  of  crystalline  rocks  and  their 
origin  is  due  to  the  union  of  certain  substances  which  separ- 
ate out  of  the  mass  and  combine, — not  in  a  haphazard  way, 
but   in  strict  accordance   with   natural   laws.     When   these 
combined  substances  are  forced  up  into  the  cooler  crust,  by 


92      PRACTICAL  GEOLOGY  AND  MINERALOGY 

the  eruptive  forces,  they  crystallize  and  take  on  that  definite 
form,  composition  and  structure  known  as  minerals.  The 
proof  of  this  is,  that  many  minerals  may  be  formed  in  the 
laboratory.  For  example,  if  we  take  two  substances,  sulphur 
and  iron  filings,  in  the  proportion  of  four  grains  sulphur  to 
seven  grains  iron,  add  warm  water,  soon  the  mass  begins  to 
swell,  turns  blackish  and  forms  a  new  body,  neither  iron  nor 
sulphur,  which  is  called  Iron  Sulphide.  This  is  a  common 
earth  mineral  and  since  nature's  laws  are  unchangeable,  we 
know  that  all  iron  sulphide  is  formed  in  the  same  manner. 

If  any  other  proportions  of  iron  and  sulphur  are  taken, 
some  of  either  the  iron  or  the  sulphur  will  be  left  over  in 
its  native  state,  as  it  can  not  enter  into  the  new  body  except 
in  the  proportions  named.  This  is  called  a  Chemical  Com- 
bination, and  this  same  principle  underlies  the  formation  of 
all  minerals. 

What  is  Mineralogy? 

4.  MINERALOGY  is  the  science  which  treats  of  Min- 
erals, and  as  usually  presented,  includes  the  study  of  their 
composition,  physical  properties  and  chemical  characteristics, 
but  the  latter  properly  belongs  to  Chemistry,  so  nothing 
but  a  few  basic  principles  of  Chemistry  will  be  considered 
here. 

More  than  one  thousand  minerals  have  been  discovered 
and  classified  by  mineralogists,  but  90  per  cent,  of  these  are 
of  scant  interest  to  the  mining  man.  Twenty  minerals  of 
first  importance  make  up  nine-tenths  of  the  earth's  crust. 
Only  those  minerals  that  occur  in  quantities  to  make  them 
of  commercial  importance,  or  those  that  are  associated  with 
mineral  deposits  will  have  extended  consideration  under  this 
subject. 


MINERALOGY  93 


What  are  Elements? 

5.  Nearly  all  minerals  are  compounds, — that  is,   they 
are  composed  of  two  or  more  substances,   which  makes  a 
knowledge  of   each   component   part   necessary   in   order  to 
satisfactorily     determine       the     identity     of  a  mineral  and 
classify  it. 

The  Ancients  divided  all  matter  into  four  classes,  Earth, 
Air,  Fire,  Water,  and  called  these  elements.  Science,  how- 
ever, does  not  recognize  these  as  Elements  at  all.  Water 
and  Air  are  made  up  of  gases.  Fire  results  from  the  union 
of  several  elements,  while  the  Earth  itself  comprises  all  the 
elements. 

AN  ELEMENT  is  defined  to  be  a  substance  that  can  not 
be  divided  or  separated  into  simpler  substances  by  any  known 
process ;  in  a  word  it  is  one  of  the  primary  forms  of  matter. 

At  the  present  time  there  are  about  eighty  recognized 
simple  substances  called  Elements.  Several  of  these  have 
been  discovered  within  the  last  half  centeury  and  we  have 
good  reason  to  believe  that  some  substances  now  classed  as 
elements  may  be  shown  in  the  future  to  be  compounds  of 
two  or  more  simpler  substances.  A  full  discussion  of  Ele- 
ments belongs  to  Chemistry,  but  inasmuch  as  the  study  of 
Minerals  involves  some  knowledge  of  Elements  this  subject 
must  have  brief  attention  here. 

NATIVE  ELEMENTS  are  those  that  are  found  at  times 
free  in  nature.  There  are  fifteen  of  these,  the  remaining 
sixty-three  elements  have  never  been  found  except  in 
combination  with  one  or  more  elements. 

What  are  Compounds? 

6.  A  COMPOUND  is  made  up  of  two  or  more  simple 
elements.     While   a   few  elements   occur   free,   these  same 


94       PRACTICAL  GEOLOGY  AND  MINERALOGY 


elements   are    found    in    greater    abundance   combined    with 
other  elements  and  are  then  called  Compounds. 

What  are  Symbols  and  Formulas? 

7.  A  SYMBOL  is  a  short  method  of  expressing  an  ele- 
ment,— in  other  words,  an  abbreviation.  Many  elements 
are  expressed  by  the  first  letter  in  the  name,  as  O,  the 
symbol  of  Oxygen.  When  several  elements  have  the  same 
initial  another  letter  in  the  name  is  added  to  distinguish  it, 
as  Os,  the  symbol  for  the  element  Osmium.  Most  symbols 
are  abbreviations  of  the  English  words,  but  the  metals  known 
to  the  Ancients  have  symbols  derived  mainly  from  the  Latin 
or  Greek.  Fe  is  the  symbol  for  Iron,  from  the  Latin 
Ferrum.  The  symbol  for  Gold  is  Au,  from  the  Latin 
Aurum. 

A  FORMULA  is  a  combination  of  symbols,  and  as  applied 
to  a  mineral,  expresses  in  a  brief  way  all  the  elements  that 
enter  into  the  compound.  For  example:  Quartz  is  a  com- 
pound, made  up  of  two  elements  Silicon  and  Oxygen,  Si  is 
the  symbol  for  Silicon,  and  O  is  the  symbol  for  Oxygen, 
combined  we  have  (SiO2)  the  formula  for  Quartz. 

This  formula  conveys  to  us  the  information  that  Quartz 
is  composed  of  one  volume  of  Silicon  and  one  volume  of 
Oxygen,  the  number  2  below  the  O,  signifies  that  the  Oxy- 
gen volume  consists  of  two  parts  or  atoms. 


MINERALOGY  95 


Mineralogists  have  arranged  formulas  for  nearly  all 
mineral  compounds,  which  show  at  a  glance  all  the  elements 
in  the  compound,  and  with  a  knowledge  of  their  combining 
weight  of  each  the  proportions  or  percentage  of  each  element 
can  be  calculated. 

How  are  Elements  Classified? 

8.  Since  the  Eighteenth  Century,  it  has  been  customary 
to  divide  elements  into  two  classes  (1)  Metals  and  (2) 
Metalloids.  The  ending  oid  means  like  or  resembling,  and 
Metalloids  are  so  named  because  they  resemble  metals  in 
some  of  their  properties.  In  fact  the  resemblance  is  some- 
times so  close  that  it  is  hard  to  draw  a  line  to  distinguish 
the  two  classes.  If  metalloids  possessed  a  metallic  appearance, 
they  might  be  classed  as  metals.  Combinations  of  metalloids 
form  acids. 

Modern  Classification  of  Elements 

Later    authorities    now    divide    elements    into    three 
classes,  viz: 

(1)  Metals. 

(2)  Semi-Metals. 

(3)  Non-Metals. 

The  following  table,  consisting  of  forty-eight  elements, 
includes  about  all  that  are  of  particular  interest  to  the  min- 
ing man.  The  rarer  elements,  of  which  there  are  about 
thirty  additional,  are  outside  the  purview  of  this  book  and 
hence  do  not  merit  consideration  here. 


96       PRACTICAL  GEOLOGY  AND  MINERALOGY 


COMMON 

MINERAL   ELEMENTS 

NAME                      SYMBOL 

NAME                      SYMBOL 

Aluminum 

Al 

t  Molybdenum 

Mo 

Antimony  (  L.Stibium 

)   Sb 

Nickel 

Ni 

Arsenic 

As 

*Nitrogen 

N 

Barium 

Ba 

Osmium 

Os 

t  Bismuth 

Bi 

*Oxygen 

0 

Boron 

B 

Palladium 

Pd 

%Eromine 

Br 

Phosphorus 

P 

Cadmium 

Cd 

Platinum 

Pt 

Calcium 

Ca 

Potassium    (  Kalium  ) 

K 

Carbon 

C 

Selenium 

Se 

*Chlorine 

Cl 

Silicon 

Si 

Chromium 

Cr 

Silver   (Argentum) 

Ag 

Cobalt 

Co 

Sodium    (Natrum) 

Na 

Copper   (L.Cuprium) 

Cu 

Strontium 

Sr 

*  Fluorine 

Fl 

Sulphur 

S 

Gold   (L.  Aurum) 

Au 

fTantalum 

Ta 

^Hydrogen 

H 

^Tellerium 

Te 

Iodine 

I 

Tin    (L.  Stannum) 

Sn 

Iridium 

Ir 

fTitanium 

Ti 

Iron    (L.  Ferrum   ) 

Fe 

fTungsten  (Wolfram) 

W 

Lead   (L.  Plumbum) 

Pb 

Uranium 

Ur 

Magnesium 

Mg 

fVanadium 

V 

Manganese 

Mn 

fZinc 

Zn 

\  Mercury  (Hydrar- 

gyrum) 

Hg 

Zirconium 

Zr 

The  names  printed  in  Italics  are  classed  as  Metalloids. 
*Signifies  Gaseous  element. 
tSometimes  classed  as  Semi-Metals. 
^Liquid  at  ordinary  temperatures. 


MINERALOGY  97 


How  are  Minerals  Grouped? 

8.  Minerals    are    grouped    according    to    the    principal 
element  in  their  composition  as  follows: 

(a)  Oxides  (j)   Carbonates 

(b)  Sulphides  (k)   Silicates 

(c)  Arsenides  (1)   Nitrates 

(d)  Antimonides  (m)  Borates 

(e)  Tellurides  (n)   Phosphates 

(f)  Chlorides  (o)    Molybdates 

(g)  Iodides  (p)   Vanadates 
(h)   Bromides  (q)   Tungstates 
(i)   Fluorides 

What  Do  the  Endings  Signify? 

9.  The  older  authorities  used  the  endings,  ide,  ate  and 
ite,  in  various  ways,  but  they  are  now  used  generally  to 
signify    certain    groups    of    minerals.      The    ending    ide    is 
used  to  denote  the  union  of  two  elements  in  a  compound, 
the  ending  ate  denotes  a  union  of  three  or  more  elements  in 
a  compound. 

The  ending  ite  was  used  for  ide  as  in  Sulphide,  but  now 
seldom  used  in  this  way.  Ite  is  a  common  ending  of  many 
minerals,  especially  those  that  are  named  after  their  dis- 
discoverers,  like  Jamesonite,  etc. 

Oxides 

10.  OXYGEN    (O)   is  a  gaseous  element,  so  abundant 
that  it  constitutes  about  one-fifth  of  the  atmosphere,  eight- 
ninths  of  water  by  weight  and  nearly  half  of  the  Earth's 
solid  crust.     Oxygen  forms  compounds  with  all  other  ele- 
ments except  Fluorine  and  enters  into  the  composition  of 
most  all  minerals  in  the  Oxide  Zone. 

The  union  of  Oxygen  with  another  element  produces 
Oxides,  which  form  an  important  group  of  minerals.  When 


98      PRACTICAL  GEOLOGY  AND  MINERALOGY 

certain  elements  as  sulphur  (S),  Carbon  (C),  Phosphorus 
(P),  and  Iron  (Fe),  are  brought  into  contract  with  Oxygen 
at  suitable  temperatures,  they  burn  evolving  heat  and  produce 
oxides  of  these  substances.  Oxygen  is  intensely  active  and 
unites  with  other  elements  in  different  proportions  owing  to 
the  conditions  present.  The  principal  group  of  minerals  thus 
formed  are  called  Oxides ;  the  sub-groups  of  minerals  ending 
in  ate  are  called  Oxygen  Salts. 

PRINCIPAL  OXIDE  MINERALS 

MINERAL  FORMULA  NAME 

Water  (H2O)  Hydrogen  Oxide. 

Quartz  (SiO2)  Silicon  Oxide. 

Cuprite  (Cu2O)  Copper  Oxide. 

Zincite  (ZnO)  Zinc  Oxide. 

Lime  (CaO)  Calcium  Oxide. 

Corundrum  (A2O3)  Aluminum  Oxide 

Hematite  (Fe2O3)  Iron  Oxide. 

Minium  (PbO)  Lead  Oxide. 

Manganosite  (MnO)  Manganese    Oxide. 

Arsenolite  (As2O3)  Arsenic  Oxide. 

Bismite  (Bi2O3)  Bismuth  Oxide. 

Valentinite  (Sb2O3)  Antimony   Oxide 

Tellurite  (Te2O3)  Tellurium  Oxide. 

Tungstite  (WO3)  Tungsten  Oxide. 

Cassiterite  (SnO2)  Tin  Oxide. 

Rutile  (TiO2)  Titanium  Oxide. 

Periclase  (MgO)  Magnesium  Oxide. 

Sulphides 

11.  SULPHUR  is  an  element  found  native  in  volcanic 
districts.  When  sulphur  enters  into  a  combination  with 
another  element  it  produces  what  are  called  Sulphides. 
Sulphur  combined  with  two  or  more  elements  produces 
Sulphates. 


MINERALOGY 


99 


Nearly  all  Minerals  found  below  the  natural  water  level 
are  Sulphides,  hence  the  name  Sulphide  Zone. 


PRINCIPAL  SULPHIDE  MINERALS 


MINERAL 

Argentite 

Galena 

Chalcocite 

Sphalerite 

Cinnabar 

Millerite 

Marcasite 

Realgar 

Stibnite 

Bismuthinite 

Molybdenite 

Patronite 


Barite 

Celestite 

Anglesite 

Gypsum 

Epsomite 

Alunogen 


FORMULA 

(Ag2  S) 

(PbS 

(Cu2S) 

(ZnS) 

(HgS) 

(NiS) 

(FeS2) 

(AsS) 

(Sb2S8) 

(BitS.) 

(MoS) 

(VS4) 


NAME 

Silver  Sulphide. 
Lead  Sulphide. 
Copper   Sulphide. 
Zinc  Sulphide. 
Mercury  Sulphide. 
Nickel  Sulphide. 
Iron  Sulphide. 
Arsenic   Sulphide. 
Antimony  Sulphide. 
Bismvith  Sulphide. 
MolybdenumSulphide 
Vanadium  Sulphide. 


SULPHATE    MINERALS 


(BaSO4) 

(SrS04) 

(PbSOJ. 

(CaSOJ 

(MgSOJ 

(A12S04) 


Barium   Sulphate. 
Strontium  Sulphate 
Lead  Sulphate. 
Calcium  Sulphate. 
Magnesium  Sulphate. 
Aluminum  Sulphate. 


Arsenides 

12.  ARSENIC  (As)  is  an  element  often  found  native  in 
primitive  rocks,  which  fact  often  puzzles  the  miner  and 
prospector.  This  element  enters  into  compounds  forming 
Arsenide  Minerals. 

Niccolite  (NiAs)   Nickel  Arsenide. 
Smaltite   (CoAs2)    Cobalt  Arsenide. 
Domeykite  (Cu3As)  Copper  Arsenide. 
S  perry  lite  ( Pt  As2 )  Platinum  Arsenide. 


100     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Compounds  of  Arsenic,  Sulphur  and  other  elements  are 
sometimes  classed  as  Sulph-arsenites. 

Antimonides 

13.  ANTIMONY  (Sb)  occurs  native  and  is  then  known 
as    Gray   Antimony.      It    enters    into    combination    with    a 
number  of  elements  forming  Antimonides. 

PRINCIPAL    ANTIMONIDE    MINERALS 

Stibnite  (Sb2S3)  Antimonide  of  Sulphur. 

Dyscrasite  (Ag3Sb)  Antimonide  of  Silver. 

Horsfordite  (Cu  Sb)  Antimonide  of  Copper. 

Breithauptite   (Ni  Sb)  Antimonide  of  Nickel. 
Antimony    forms    compounds    with    Sulphur    and    other 
elements,   which   are  classed   as   Sulph-Antimonates.      Com- 
pounds of  Antimony  with  oxygen  and  another  element  are 
called  Antimonates,  also  Antimonites. 

Tellurides 

14.  Tellurium  (Te)  is  an  element  that  is  never  found 
native,  but  forms  compounds  with  other  elements  known  as 
Tellurides.    This  element  has  no  present  value  in  itself,  but 
is  associated  with  very  rich  metal  ores. 

PRINCIPAL   TELLURIDE    MINERALS 

Sylvanite  ( Au  Te,  Ag)   Gold  and  Silver  Telluride. 
Krennerite   (Au  Te)    Gold  Telluride. 
Hessite  (AgTe)  Silver  Telluride. 
Tetradamite   (BiTe)   Bismuth  Telluride. 
Coloradoite   (HgTe)    Mercury  Telluride. 
Altaite   (PbTe)    Lead  Telluride. 
Melonite  (NiTe)  Nickel  Telluride. 
Nagyagite    (AuPbSbTeS)    Telluride. 

Chlorides 

15.  Chlorine    (C)    is  a  gaseous  element   never   found 
free,  but  always  combined  with  other  elements  and  forms 
Chlorides.     It  is  a  solvent  for  gold. 


MINERALOGY  101 


PRINCIPAL  CHLORIDE   MINERALS 

Halite  (NaCl)   Sodium  Chloride. 
Calomel  (HgCl)  Merucuy  Chloride. 
Cerargyrite    (AgCl)    Silver  Chloride. 
Atacamite   (CuCl)    Copper  Chloride. 
Sylvite  (KC)  Potassium  Chloride. 
Sal  Ammoniac   (N  H  Cl)   Ammonium  Chloride. 

Iodides 

16.  Iodine  (I)  is  a  solid  element  which  combines  to 
form  a  few  minerals,  called  Iodides.  The  following  are  the 
principal  minerals: — 

lodyrite  (Agl)   Iodide  of  Silver. 

Marshite  (Cu  I)   Copper  Iodide. 

Bromides 

16.  Bromine   (Br)   is  a  liquid  element  which  combines 
with  Chlorine  and  Iodine  to  form  a  few  compounds,  viz: 

Bromyrite  (AgBr)  Bromide  of  Silver. 
Embolite    (Ag,  Cl,  Br)    Silver  Chloro-Bromide. 

Fluorides 

17.  Fluorine    (Fl)    is    a    gaseous    element    that    unites 
with  other  elements  to  form  a  few  minerals  as  follows: — 

Fluorite  (CaFl)   Calcium  Fluoride. 
Cryolite  (NaAlFl)  Fluoride  of  Sodium  and 

Aluminum. 
Sellaite   (MgFl)    Magnesium  Fluoride. 

Carbonates 

18.  The  element  Carbon   (C)   is  found  native  crystal- 
lized in  the  Diamond  and  in  a  modified  form  in  Graphite. 
Charcoal  and  Coal  are  common  forms  of  Carbon.     Carbon 
unites  with  Oxygen  and  metallic  elements  to  form  an  im- 
portant group  of  minerals  known  as  Carbonates. 


102     PRACTICAL  GEOLOGY  AND  MINERALOGY 


PRINCIPAL    CARBONATE    MINERALS 

Calcite   ( Ca  C  O^  Calcium  Carbonate. 


Siderate    (FeCQi   Iron  Carbonate. 
Smithsonite  (ZnCO3)   Zinc  Carbonite. 
Strontianite   (Sr"CO3)    Strontium  Carbonate. 
Azurite    (CuCO3)    Copper   Carbonate. 
Rhodochrosite   (MnCO^)    Magnesium  Carbonate. 
Witherite  (BaCO3)   Barium  Carbonate. 
Cerussite  ( Pb  C  O3 )    Lead  Carbonate. 
Natron    (N*uCO3)    Sodium   Carbonate. 
Bismutite   (BI  C  G}   Bismuth  Carbonate. 

Silicates 

19.  The  element  Silicon  (Si)  is  never  free,  but  always 
combined  with  Oxygen.  Quartz,  the  Oxide  of  Silicon,  is 
commonly  called  silica,  and  when  three  elements  enter  into 
the  combination,  Silicates  are  formed.  Next  to  Oxygen, 
Silicon  is  the  most  plentiful  of  all  elements  and  is  the  prin- 
cipal constituent  of  all  rocks  except  coal  and  limestone. 

PRINCIPAL  SILICATE  MINERALS 

Crysocolla  (CuSiO3)   Copper  Silicate. 
Garnierite   (NiMgSi,  Etc.)    Nickel  Silicate. 
Kaolinite   ( Al  Si  Oj^  Aluminum  Silicate. 


Talc  (Mg  Si  O}  ./Magnesia  Silicate. 
Calamine   (Zn  Si  O,  Etc.)   Zinc  Silicate. 
Actinolite    (CaMgFeSiO)    Calcium   and    Magne- 
sium Silicate. 

Orthoclase  (K,  Al  Si  O)  Potash  Silicate. 
Albite  (Na,  Si,  Al,  O,  Etc.)  Sodium  Silicate. 

Nitrates 

20.  NITROGEN  (N)  is  a  very  abundant  element,  con- 
stituting four-fifths  of  the  atmosphere  by  bulk,  combined  with 
Oxygen.  When  alone,  Nitrogen  is  inactive, but  the  few  com- 


MINERALOGY  103 


pounds  into  which  it  enters  are  the  most  energetic  known. 
The  principal  Nitrates  are  as  follows: 

Soda  Niter  (NaNO3)   Sodium  Nitrate. 

Niter  (Saltpeter  KNO3)   Potash  Nitrate. 

Gerhardite  (CuNO^etc.)  Copper  Nitrate. 

Nitrobarite   (BaNO^etc.)   Barium  Nitrate. 

Borates 

21.  The  element  Boron  (B)  is  found  in  nature  in  the 
form  of  a  salt  known  as  Borax   (Na,  BO).     Two  other 
compound   minerals   are   important,   viz: — 

Colmantte  (CaBO,  etc.)   Borate  of  Lime. 
Boracite  (B,  Mg,  O,  Cl,  etc.)  Magnesium  Borate. 

Phosphates 

22.  PHOSPHORUS   (P)   is  never  found  free  in  nature, 
but  forms  compounds  with  a  few  elements  and  the  minerals 
which  are  known  as  Phosphates: — 

Apatite   (P,  Ca,  Cl,  O,  etc.)    Calcium  Phosphate. 
Pyromorphite    (P,  Cl,  O,  Pb)    Lead   Phosphate. 

NOTE:  Phosphate  of  Lime  is  the  result  of  animal  ac- 
cumulations of  bones,  etc. ;  deposits  of  Guano  are  valuable 
as  fertilizers.  The  Phosphate  minerals  named  no  doubt 
receive  their  Phosphorus  content  /from  dissolved  animal 
matter. 

Tungstates 

23.  The  element    Tungsten    (Wolfram,  W)    is  never 
found  free,  but  always  in  combination  with  a  few  elements 
forming  Tungstates,  as  follows: — 

Wolframite    (W,  Fe  Mn  O)    Iron  Tungstate. 
.    Scheelite    (W,  CaO)    Calcium  Tungstate. 
Hubnerite   (W,  Mn  O)    Manganese  Tungstate. 
Stolzite  (W,  PbO)  Lead  Tungstate. 


104     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Molybdates 

24.  MOLYBDENUM   (Mo)  is  an  element  that  is  found 
only  in  a  few  compounds  known  as  Molybdates,  as  follows : 

Wulfenite  (MoPbO)  Lead  Molybdate. 

Powelite  (MoCaO)   Calcium  Molybdate. 
NOTE:  The  chief  ores  of  Molybdenum  are  Wulfenite 
and  Molybdenite  (Mo  S2)  ;  the  latter  is  grouped  under  Sul- 
phides (Par.  11). 

Vanadates 

25.  VANADIUM    (V)    is  a  rare  element  and  combines 
with  only  a  few  elements  to  form  Vanadates.    This  element 
is  usually  associated  with  Lead. 

Vanadinite  (VPbCIO)  Lead  Vanadate. 
Descloizite  (V  Pb)   Lead  Vanadate. 
NOTE:  Vanadium    occurs    in    the    mineral    Roscoelite 
(VMnSiFe,  etc.)  as  a  Silicate. 

What  Are  Known  as  Alikali  Minerals? 

26.  The  elements  Sodium,  Potassium,  Calcium,  Barium 
and  Magnesium  are  the  principal  Alkali  Minerals.     They 
are  generally  soluble  in  water,  giving  it  a  soapy  taste  and 
feel.      Alkali    restores    the    blue    color    to    vegetable    blues 
(Litmus)  that  have  turned  red  from  acids,  in  other  words 
alkalies  neutralize  acids.     The  Alkali  minerals  are  mainly 
Chlorides,    Carbonates,    Nitrates   and    Sulphates,    and    have 
been  mentioned   under  those  groups.     Alkali   minerals  are 
metallic  or  basic. 

What  Are  the  Acid  Minerals? 

27.  AN  ACID  is  the  exact  opposite  of  an  alkali,  and  has 
the  property  of  changing  Vegetable  blues   (Lit mas)   to  red 
tints.     Quartz  is  the  most  common   acid   mineral.     Com- 


MINERALOGY  105 


pounds  of  Arsenic,  Antimony,  Bismuth,  Sulphur,  Tellurium, 
Boron,  Molybdenum,  Tungsten  and  Vanadium  are  usually 
classed  Acid  Minerals. 


PHYSl^JL  PROPERTIES  OF  MINERALS 

28.  The  Physical  properties  of  minerals  are  those  that 
we  may  observe  by  the  Physical  Senses, — Touch,  Taste, 
Smell  and  Sight.  In  examining  a  mineral  these  senses  con- 
vey certain  impressions  to  the  mind,  which  makes  certain 
inferences  or  draws  conclusions  more  or  less  imperfect, 
according  to  one's  knowledge  and  skill,  which  can  only  be 
acquired  by  practice. 

(a)  TOUCH,  or  Feel,  is  the  sense  that  enables  one  to 
determine  if  a  substance  is  harsh,  gritty,  smooth  or  greasy, 
as  in  Silica,  Graphite,  Talc,  etc. 

(b)  TASTE.     This  is  important  only  in  a  few  minerals 
that    are    soluble    in    water.      Examples:  Halite    is    Saline 
(salty)  ;  Natron  is  alkaline  and  Carnalite  is  bitter. 

(c)  SMELL.     (Odor.)      Most    minerals   are    odorless 
under  ordinary  conditions,  but  when  struck  with  a  sharp 
instrument  or  heated,  a  few  give  off  characteristic  odors. 
Example:  Arsenopyrite  "(Mispickel)  is  said  to  be  Allicious, 
that  is  gives  off  an  odor  of  Garlic;  Pyrite  emits  Sulphurous 
fumes;  Asphaltum  has  Bituminous  odor,  etc. 

(d)  SIGHT  is  the  most  important  of  the  senses  as  it  is 
by  this  that  Color,  Luster,  Fracture,  Cleavage,  Crystalliza- 


106     PRACTICAL  GEOLOGY  AND  MINERALOGY 

tion,  etc.,  are  made  possible  of  determination.     The  distinc- 
tive characteristics  of  minerals  are : 

(1)  Luster. 

(2)  Color  and  Streak. 

(3)  Hardness. 

(4)  Gravity. 

( 5 )  Fracture. 

(6)  Cleavage. 

(7)  Tenacity. 

(8)  Crystal  System. 

The  importance  of  these  properties  varies  in  different 
minerals.  For  example,  Gravity  may  distinguish  one  mineral 
more  clearly  than  all  the  other  physical  properties;  another 
mineral's  color  alone  may  be  so  characteristic  as  to  identify  it, 
but  there  are  some  mineral  compounds  that  nothing  short  of 
a  chemical  analysis  will  disclose  their  identity.  However, 
most  all  the  common  minerals  may  be  determined  off-hand 
by  these  physical  properties. 

(1)   Luster 

29.  The  Luster  of  a  mineral  is  due  to  the  reflection  of 
light  on  its  surface.  There  are  several  degrees  of  luster  as 
follows : — 

(a)  Metallic  is  the  luster  of  metal,  but  if  the  resem- 
blance to  metal  is  only  slight,  it  is  said  to  be  Sub-metallic. 

(b)  Vitreous  is  the  term  used  to  denote  glassy  luster. 

(c)  When  it  has  the  luster  of  rosin   it  is  said  to  be 
Resinous. 

(d)  Greasy  when  it  looks  like  smeared  with  oil. 

(e)  Pearly,  when  the  luster  of  a  pearl. 

(f)  Silky,  when  like  silk. 


MINERALOGY  * 


107 


(g)   Adamantine  is  the  luster  of  the  Diamond, 
(h)   Earthy  or  dull  is  the  term  used  when  there  is  no 
luster  at  all. 

(2)   Color 

30.  The  Color  of  a  mineral  often  affords  a  good  means 
of  identification.  Some  minerals  when  powdered  give  a 
Streak  (color)  different  from  the  color  of  the  specimen  as  a 
whole.  The  streak  color  may  be  obtained  by  drawing  a 
projecting  point  of  the  mineral  specimen  across  a  piece  of 
unglazed  porcelain,  or  a  streak  plate,  but  the  characteristic 
streak  color  is  best  obtained  by  pulverizing  the  mineral  and 
rubbing  the  powdered  pulp  with  the  tip  of  finger  on  a  white 
unglazed  paper.  The  following  are  the  characteristic  col- 
ors of  the  principal  minerals: 

DISTINCTIVE  MINERAL  COLORS 


RED 

Rose-Red Rose   Quatrz 

Orange-Red     Wulfenite 

Purplish-Red     ....  Cinnabar 

Brick- Red    Jasper 

Blood-red    Zincite 

GREEN 

Olive-Green    Olivine 

Sage-Green    Serpentine 

Sea-Green    Fluorite 

Apple-Green     .  .  .  Garnierite 
Grass-Green    ....  Malachite 

VIOLET 

Reddish-Violet     .  .  Amethyst 
Bluish- Violet    Sodalite 

GRAY 

Smoke-Gray    ....  Limestone 
Bluish-Gray    .  .  .  .Anhydrate 


YELLOW 

Orange- Yellow    .  .  Orpiment 

Ochre-Yellow    Ochre 

Resin- Yellow    Opal 

Honey- Yellow    Calcite 

Brownish-Yellow,    Dolomite 
BLUE 

Indigo-Blue    Covelite 

Sky-Blue    Cyanite 

Greenish-Blue    .  Chrysocolla 

Azure-Blue    Lazurite 

BROWN 

Clove-Brown    ....  Limonite 
Yellowish-Brown    .  .  .Wood 
Opal. 

WHITE 
Snow-white    ....  Magnesite 

Reddish-white    Barite 

Greenish-white    .          .  Talc 


108     PRACTICAL  GEOLOGY  AND  MINERALOGY 

METALLIC   COLORS 

Lead-Gray    .  . .  Molybdenite      Silver-white    .  ,  Arsenopyrite 
Bronze- Yellow    .  .  Pyrrhotite      Brass  -Yellow    .  Chalcopyrite 

(3)    Hardness 

31.  THE  HARDNESS  of  a  mineral  is  that  property 
which  enables  it  to  scratch  or  be  scratched,  but  does  not  have 
reference  to  the  breaking  of  a  mineral  itself.  Hardness  is 
determined  by  comparison  with  other  minerals  used  as  a 
standard.  The  following  scale  is  used  by  all  mineralogists : 

SCALE    OF    HARDNESS 

(1)  TALC.     The  softest  mineral  easily  scratched  with 
finger  nail. 

(2)  GYPSUM.     The    finger    nail    scratches    with    diffi- 
culty.    A  copper  coin  scratches  Gypsum,   but  it  will   not 
scratch  copper. 

(3)  CALCITE.     Can  not  be  scratched  with  finger  nail. 
It  will  scratch  pure  copper  as  well  as  Gypsum. 

(4)  FLUORITE.     Can   not   be   scratched     with    copper 
coin.     An  ordinary  pin  will  not  scratch  it.     The  point  of  a 
knife  will  scratch  Fluorine  easily. 

(5)  APATITE.     Will     scratch     Fluorite     or     Calcite, 
Scratches    glass    with   difficulty.      Is    easily    scratched     by 
knife. 

(6)  FELDSPAR      (Orthoclase     or     Serpentine).      Will 
scratch   glass;   can   be   scratched   with   point   of   knife   with 
difficulty. 

(7)  QUARTZ.     Can  not  be  scratched  with  knife;  yields 
with  difficulty  to  a  file ;  scratches  glass  easily. 

(8)  TOPAZ.     Scratches  quartz  and  most  other  minerals. 


MINERALOGY  109 


(9)  CORUNDRUM.     Nothing     but     a     Diamond     will 
scratch  Corundrum  and  all  other  minerals  yield  to  it. 

(10)  DIAMOND.     The  hardest  known  mineral;  scratch- 
es all  minerals. 

Any  mineral  in  this  scale  will  scratch  all  in  the  scale 
below  it,  but  will  scratch  no  mineral  above  it.  Quartz  or 
flint  is  common  everywhere,  and  may  be  used  as  a  standard ; 
anything  that  can  be  scratched  with  a  sharp  corner  of  quartz 
is  below  7  in  the  scale  of  hardness. 

IN  PRACTICAL  FIELD  TESTS,  the  finger  nail,  a  copper 
coin,  the  point  of  a  knife  and  a  piece  of  flint  will  enable  one 
to  determine  the  hardness  of  most  any  mineral,  likely  to  be 
found. 

TABLE   OF    HARDNESS    OF   COMMON    MINERALS 

No.  1  TO  1.5 

Minerals  that  can  be  scratched  with  finger  nail: — 
Nagyagite  Sternbergerite  Cerargyrite 

Embolite  Lead  Calomel 

Nitratine  Molybdenite  Arsenolite 

Elaterite  Ozocerite  Talc 

No.  2  TO  2.5 

Minerals  that  scratch  with  ringer  nail  with  great  difficul- 
ty, but  are  easily  scratched  with  a  copper  coin: — 

Sylvanite  Calaverite  Krennerite 

Argentite  Pyrargyrite  Proustite 

Stephenite  Bromyrite  Galena 

Jamesonite  Minium  Vanadinite 

Cinnabar  Pyrolusite  Tobernite 

Brucite  Gypsum  Sylvite 

Borax  Niter  Tellurium 

Orpiment  Realgar  Bismuth 

Tetradymite  Graphite  Gilsonite 

Bituminous  Coal       Muscovite  Kaolinite 


110     PRACTICAL  GEOLOGY  AND  MINERALOGY 

No.  3  TO  3.5 

Minerals  that  will  scratch  Copper  and  Gypsum,  viz: — 

Stromeyerite              Antimony  Barite 

Domeykite                 Hessite  Chalcocite 

Cuprite                      Tetrahedrite  Altacamite 

Crysocolla                  Olivenite  Anglesite 

Pyromorphite            Altaite  Sphalerite 

Millerite                    Cerussite  Coloradoite 

Magnesite                  Genthite  Calcite 

Aragonite                   Dolomite  Arsenic  (native) 

No.  4  TO  4.5 

Minerals  a  pin  will  not  scratch  but  the  point  of  a  knife 
scratches  easily: — 

Azurite                      Wolfenite  Zincite 

Calamine                   Iron  Pyrrhotite 

Siderite                       Rhodochrosite  Stannite 

Scheelite                     Fluorite  Colmanite 

No.  5  TO  5.5 

Minerals   that   will   scratch    Calcite   and    Fluorite,    but 
scratch  glass  with  great  difficulty: — 

Dioptase                     Smaltite  Cobaltite 

Niccolite                    Arsenopyrite  Hematite 

Willemite                   Magnetite  Chromite 

Limonite                     Manganosite  Uranite 

Hubernite                  Wolframite  Apatite 

Pyroxine                    Amphibole  Hornblende 

Titanite                     Natrolite  Smithsonite 

No.  6  TO  6.5 

Minerals  that  will  scratch  glass  and  can  be  scratched 
with  point  of  knife  only  with  difficulty: 

Franklinite                 Pyrite  Vessuvianite 

Rutile                         Turquoise  Sodalite 

Garnet                       Epidote  Chrysolite 

Andesite                     Albite  Orthoclase 

Cyanite                       Marcasite  Cassiterite 

Opal                           Serpentine  Zolsite 


MINERALOGY  111 


No.  7  TO  7.5 

Minerals  that  scratch  glass  easily  and  do  not  yield  to 
knife:— 

Quartz  Amethyst  Agate 

Flint  Jasper  Zircon 

Hyacinth  Tourmaline  lolite 

No.  8  TO  8.5 

Minerals  that  will  scratch  quartz  and  most  all  other 
minerals : — 

Beryl  Topaz  Spinel 

Chrysoberyl  Almandine  (Ruby)    Disluite 

No.  9 

Corundrum  Sapphire  Oriental  Ruby 

Oriental  Topaz        Oriental  Emerald     Oriental  Amethyst 

(4)   Specific  Gravity 

32.  This  property  is  next  in  importance  to  Hardness. 
It  refers  to  the  weight  of  a  substance  using  water  as  a 
standard  of  comparison,  which  is  taken  as  the  unit  or  1 ;  if 
the  Specific  Gravity  of  a  mineral  is  given  as  2  then  we  under- 
stand it  is  twice  as  heavy  as  the  same  volume  of  water.  If 
gravity  is  3,  then  the  mineral  is  three  times  the  weight  of 
water,  and  so  on. 

The  rule  to  determine  Specific  Gravity  is  to  weigh  the 
substance  in  air,  then  weigh  it  in  water.  Divide  the  weight 
in  air  by  the  loss  of  weight  in  water,  and  the  quotient  is  the 
Specific  Gravity.  A  simple  method  of  determining  Gravity 
is  to  attach  the  mineral  to  a  silk  thread,  which  will  enable  it 
to  be  weighed  in  air  and  water.  For  example,  if  a  piece  of 
mineral  weighs  4  oz.  in  air,  and  3  oz.  suspended  in  water, 
the  difference  is  1  oz. ;  this  divided  into  4,  the  weight  in  air, 
gives  the  Specific  Gravity  as  4. 


112     PRACTICAL  GEOLOGY  AND  MINERALOGY 

A  PRACTICAL  FIELD  METHOD  where  weighing  is  out  of 
the  question  and  for  an  approximate  determination,  take  a 
piece  of  quartz  or  granite,  the  Gravity  of  which  is  2.5  to  2.8. 
Nearly  all  the  metal  minerals  are  heavier  than  quartz.  If  a 
specimen  of  equal  size  appears  twice  as  heavy  as  quartz,  you 
can  safely  conclude  that  its  Gravity  is  5  or  better.  If 
weight  is  about  half  more  then  gravity  w^ould  be  4  or  less. 
An  accurate  determination  of  Gravity  is  seldom  required  in 
the  study  of  minerals. 

The  following  is  the  approximate  Specific  Gravity  of 
minerals  that  may  be  used  as  standards  of  comparison,  viz: 

SPECIFIC  GRAVITY 

Anthracite  1.6  Sphalerite  4.0  Wolframite  7.1 

Opal  2.1  Malachite  4.0  Galena  7.5 

Gypsum  2.3  Witherite  4.3  Argentite  7.8 

Quartz  2.7  Pyrite  5.0  Cinnabar  8.0 

Cryolite  3.0  Arsenopyrite  6.0  Sylvanite  8.3 

Apatite  3.2  Smaltite  6.2  tlraninite  9.2 

Limonite  3.8  Cassiterite  6.7  Sperrylite  10.6 

(5)   Fracture 

33.  The  term  Fracture  is  used  to  describe  the  kind  of 
surface  left  exposed  from  breaking  a  mineral,  not  along  the 
regular  cleavage  plane.  There  are  three  kinds  of  fracture 
in  minerals  as  follows: — 

(a)  Conchoidal  (Cone — A  Shell).     When  a  fractured 
mineral   leaves  curved   shell-like  surfaces,   it   is  said   to  be 
Conchoidal.     Example:  Quartz. 

(b)  Even  is  the  term  used  to  denote  more  or  less  regu- 
lar  fracture,    which   is   rare.    Lithograph    Stone   has    Even 
Fracture. 

(c)  Uneven  is  the  word  used  to  describe  rough  Fractures 
as  in  Chalcocite,  Calamine  and  Pyrite. 


MINERALOGY  113 


(6)  Cleavage 

34.  Most  minerals  when  struck,  break  where  the  co- 
hesive force  is  weakest,  along  certain  planes  and  this  prop- 
erty is  called  Cleavage.     This  property  differs  in  minerals 
owing  to  the  character  of   crystals   in  the  mineral.      (See 
Crystal  Systems.) 

(7)  Tenacity 

35.  TENACITY   is   that   property   in   a   substance   that 
causes   the   particles   to  cling  together.     There   is   quite   a 
difference  in  the  tenacity  of  minerals,  but  in  any  one  sub- 
stance the  property  is  pretty  uniform.    The  different  degrees 
of  Tenacity  are  classified  as  follows : — 

(a)  BRITTLE.     This  is  a  term  used  to  show  condition 
when  a  mineral  breaks  easily  or  the  parts  separate  into  pow- 
der when  cut  with  a  knife. 

(b)  MALLEABLE.     When     mineral     can     be     cut  into 
slices  and  can  be  beaten  flat  under  a  hammer  without  flying 
to  pieces,  it  is  said  to  be  Malleable,  as  copper. 

(c)  SL-CTILE.     When  very  thin  slices  may  be  cut  off 
with  a  knife  as  in  all  malleable  minerals,  it  is  said  to  be  Sec- 
tile,  as  Embolite. 

(d)  FLEXIBLE.     When    a   substance   can    be   bent   and 
remain  so,  it  is  said  to  be  flexible.     Most  all  malleable  min- 
erals have  this  property. 

(e)  ELASTIC.     When  a  substance  returns  to  its  original 
form  after  being  bent  it  is  said  to  be  Elastic  like  Muscovite, 
or  Mica. 

(8)    Crystalline  Structure 

36.  Minerals  present  a  variety  in  structure  owing  to 
the  more  or  less  imperfect  crystallization.     The  naked  eye 


114     PRACTICAL  GEOLOGY  AND  MINERALOGY 

alone  is  often  unable  to  detect  any  crystals  in  a  mineral,  but 
the  structure  is  nevertheless  crystalline,  probably  composed 
of  minute  grains. 

There  are  a  number  of  terms  used  by  mineralogists  to 
denote  different  structures,  which  it  will  be  well  to  explain. 

(1)  COLUMNAR.     Structure    is    said    to    be    Columnar 
when  made  up  of  slender  columns.    The  varieties  of  Colum- 
nar structure  are  as  follows : — 

(a)  Fibrous.     When  columns  are  parallel  fibers  as  in 
Asbestos. 

(b)  Reticulated.     A  net-like  appearance  of  fiber. 

(c)  Stellated.     Fibers  radiating  like  star  points. 

(d)  Radiated.     When  fibers  spread  out   fan-like  as   in 
Stibnite. 

(2)  LAMELLAR.     When  structure  is  in  plates  or  leaves 
like  Mica. 

(3)  GRANULAR.     When  composed  of  fine  grain  crys- 
tals.  If  grains  are  too  small  to  be  distinguished  with  the 
naked  eye,  structuie  is  said  to  be  impalpable. 

(4)  IMITATIVE.     There  are  several  terms  used  to  des- 
cribe a  structure  which  imitates  objects,  viz: — 

(a)  Reniform — Kidney-shaped. 

( b )  Botryoidal — Grape-like. 

(c)  Mamillary — Breast-shaped. 

(d)  Dendritic — Tree-shaped. 

(e)  Capillary — Hair-like. 

( f )  Acicular — Needle-shaped. 

(g)  Stalactitic — like  Stalactites  in  caves. 

Crystal  Form 

37.     When  matter  changes  from  a  liquid  to  a  solid  state 
it  tends  to  form  into  crystals.    A  common  example  is  water 


MINERALOGY  115 


freezing  to   form  ice  and   snowflakes,   the  latter  of  which 
assumes  an  infinite  variety  of  Crystals. 

All  minerals  have  at  some  time  been  in  the  liquid  state, 
and  it  is  believed  that  originally  they  were  gases.  Whether 
the  liquid  from  which  mineral  crystals  were  formed  results 
from  dissolved  matter  (solution)  or  from  fusion  (melting), 
scientists  are  not  fully  agreed,  but  the  fact  that  crystals  are 
formed  in  the  laboratory  from  both  solutions  and  fusions, 
makes  it  reasonably  certain  that  these  are  nature's  processes 
within  the  earth.  We  know  that  gases  condense  to  liquids 
and  that  liquids  in  cooling  form  solids,  and  in  solidifying 
minerals  form  bodies  with  geometric  forms,  having  faces  and 
angles,  and  these  bodies  are  called  crystals. 

In  some  instances  these  crystals  are  so  characteristic  that 
a  mineral  may  be  identified  and  classified  by  crystals  alone. 
But  the  geologic  forces  acting  on  the  crystallizing  bodies 
compress  and  distort  them  so  that  crystals  are  drawn  out  of 
shspe  often  rendering  expert  knowledge  and  unusual  skill 
necessary  to  determine  a  crystal  definitely. 

Then  crystals  vary  in  size  in  the  same  mineral.  For 
example,  quartz  occurs  in  minute  crystals  as  well  as  of  a 
size  weighing  tons.  How  then  may  they  be  distinguished? 
No  matter  what  size  crystals  assume  there  is  always  a  uni- 
formity of  character  in. the  angles  and  faces,  that  is,  each 
edge  of  a  crystal  face,  as  well  as  the  angles  formed  where 
two  lines  meet,  always  bear  the  same  relation  to  each  other, 
whether  large  or  small.  The  measurement  of  crystals  and 
angles  is  a  delicate  operation,  impossible  to  any  one  except 
an  expert,  so  does  not  merit  consideration  here. 


116     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Crystallography 

38.  That  branch  of  Mineralogy  which  treats  of  crys- 
tal forms  is  called  Crystallography.  The  variety  of  crystal 
forms  is  almost  endless;  for  example,  the  mineral  Cuprite 
occurs  in  well  defined  cubes  and  also  in  needle  shaped  crys- 
tals, which  are  simply  cubes  elongated  or  drawn  out  but 
still  retaining  their  characteristic  angles  and  faces. 

Nothwithstanding  the  variety  in  crystals  they  have  all 
been  reduced  and  classified  under  six  forms,  viz: — 
( 1 )    Isometric. 
(2) .  Tetragonal. 

(3)  Hexagonal. 

(4)  Orthorhombic. 

(5)  Monoclinic. 

(6)  Triclinic. 

(1)  ISOMETRIC  (Equal  measure).     The  crystals  of  this 
system  are  called  Isometric,  because  the  axes  or  lines  enclos- 
ing a  crystal  face  are  of  equal  length,  and  in  their  primary 
forms  the  surfaces  are  exactly  alike. 

The  Cube  is  the  basal  form  of  this  system  and  the 
normal  type  is  found  in  Galena,  Magnetite  and  Fluorite, 
and  in  somewhat  modified  forms  in  the  minerals  Cuprite 
and  Garnet.  Gold  crystals  also  belong  to  the  Isometric 
system.  (See  Fig.  32.)  A  slightly  modified  form  of  the 
Isometric  is  found  in  the  mineral  Pyrite  shown  in  Fig.  33. 
The  faces  are  bounded  by  lines  called  axes,  which  are  of 
equal  length  and  the  angles  are  all  likewise  equal. 

(2)  TETRAGONAL.      (Four   Angles.)     The    elementary 
forms  of  this  system  are  the  square    (four-sided)    and  the 
octagon    (eight-sided)    prisms,   with  pyramids   at   each   end, 
The  mineral  Zircon  is  a  true  type  of  the  Tetragonal  system 


MINERALOGY 


117 


and  is  shown  in  Figs.  34  and  35.  The  unit  prism  is  m,  and  p 
is  the  unit  pyramid.  Two  edges  of  the  prisms  are  of  equal 
length,  the  third  is  usually  either  longer  or  shorter.  The 
unequal  axis  is  called  the  vertical  and  the  equal  axes  are 
called  the  latteral.  Pyrite,  Stolzite  and  Rutile  belong  to 
the  Tetragonal  system. 


Fig.  34 


Fig.  32.     Gold  Crystal. 
Isometric 


Fig.  36.     Apattie 


Fig.  33.     Pyrite. 
Isometric 


Fig.  35 

Zircon 

Tetragontal 


ft     m 
\ 

m 

7ig.  37.     Apatite 
Hexagonal 

(3)  HEXAGONAL.  Six  Angles.)  This  system  of  crys- 
tals closely  resembles  the  Tetragonal  execept  that  the  faces 
occur  in  multiples  of  three,  that  is  6,  9,  12,  etc.,  while  the 
Tetragonal  crystal  faces  occur  only  in  multiples  of  two,  as 
4,  6,  8,  etc.  The  elementary  crystal  forms  in  each  are  the 
prism  and  pyramid.  The  mineral  Apatite  (Figs.  36  and  37) 
is  a  representative  type  of  this  system;  the  unit  prism  is  mt 


118     PRACTICAL  GEOLOGY  AND  MINERALOGY 


forming  a  six-sided  solid.  The  unit  pyramid  is  x,  which  has 
three  axes,  the  vertical  being  at  right  angles  with  the  lateral 
axes.  The  minerals  Beryl  and  lodyrite  also  belong  to  this 
system,  and  represent  the  normal  types. 

Fig.  38.    Calcite 


Fig.  41      Quartz 
Rhombohedral 


Fig.  40.     Quartz 
Rhombohedral 


Fig.  39.     Calcite 
Rhombohedral 


There  is  a  subdivision  of  the  Hexagonal  system  that 
deserves  notice,  viz:— 

(a)  RHOMBOHEDRAL.  The  word  is  derived  from 
Rhomb  (revolve)  and  Hedral  (base).  The  crystal  faces  of 
the  Rhombohedral  are  parallelograms,  that  is,  they  have  four 
unequal  sides  and  angles,  and  there  are  three  exposed  crystal 
surfaces.  The  mineral  Calcite  is  the  natural  type  of  this 
sub-group  as  shown  in  Figs.  38  and  39.  Siderite,  Hematite 
and  Corundrum  are  Rhombohedral.  Another  type  is  shown 
in  Figs.  40  and  41,  Quartz.  The  unit  prism  is  m,  and  the 
Rhombohedron  is  r,  a  pyramid.  The  minerals  Dolomite, 
Willemite,  and  Cinnabar  have  crystals  of  the  Quartz  type. 

(4)  ORTHORHOMBIC.  (Straight-rhomb-like).  In  this 
system  the  three  axes  of  a  crystal  face  are  equal,  but  form 
right  angles  with  each  other.  The  mineral  Sulphur  is  a 
common  type  of  the  Orthorhombic  as  shown  in  Fig.  42. 


MINERALOGY 


119 


The  pyramid  is  p,  and  the  base  c.     Cerussite,  Chrysolite  and 
Calamine  are  all  modified  forms  of  the  Orthorhombic  system. 

(5)  MONOCLINIC.  (One  incline.)  The  crystals  of  this 
system  have  rectangular  bases  with  only  one  incline  of  the 
three  unequal  axes.  Gypsum  is  the  normal  type  of  the 
Monoclinic  system  shown  in  Figs.  43  and  44.  The  unit 
prism  is  m,  and  b  is  the  base. 


Fig.  42.  Sulphur 
Orthorhombic 


Gypsum 
Monoclinic 


1  nchmc 


The  minerals  belonging  to  this  system  are  numerous,  but 
the  following  are  the  most  common,  viz:  Orthoclase,  Aug- 
ite,  Hornblende,  Cryolite,  Muscovite,  Azurite,  Borax  and 
Colmanite. 

6.  TRICLINIC.  (Three  inclines).  The  axes  of  the 
Triclinic  system  are  all  unequal  and  incline  towards  one 
another,  hence  the  name.  This  system  does  not  include 
many  minerals.  The  normal  type  is  the  mineral  Abite 
(Soda  Feldspar)  shown  in  Fig.  45.  The  unit  prism  is  m, 
and  the  base  is  c\  the  connecting  angles  are  all  inclined. 
Labradorite  and  Cyanite  are  representative  types  of  this 
system. 


120     PRACTICAL  GEOLOGY  AND  MINERALOGY 

What  Causes  the  Endless  Variety  of  Crystals? 

39.  The  six  Systems  named  include  all  known  forms  of 
crystals,  but  perfect  crystals  are  not  common  and  irregular- 
ities are  so  frequent  as  often  to  require  an  expert  to  deter- 
mine their  identitiy.     This  irregularity  is  due  to  the   fact 
that  when  the  crystal  was   forming,   being  in  a  plastic  or 
wax-like    condition,    temperature    and    presssure    conditions 
prevented  it  assuming  its  normal  shape.     Crj^stals,  for  this 
reason   may   be   flattened,    drawn   out,   curved   and   twisted. 
Compound   minerals,   being  made   up   of   different   elements 
that  in  a  state  of  purity  would  tend  to  form  normal  crystals, 
result  in  an  irregular  crystalline  structure. 

What  Are  Pseudomorphs  ? 

40.  The  word  Pseudomorph  means  false  form,  and  as 
applied  to  minerals  has  a  similar  significance  to  Metamorphs 
in    rocks.      The   processes   of    crystal    change,    resulting    in 
Pseudomorphs  are  known  as: — 

( 1 )  Substitution. 

(2)  Deposition. 

(3)  Alteration. 

(1)  SUBSTITUTION.     This  is  illustrated  in  a  lime  rock 
giving  up  its  calcareous  matter  and  the  element  Silicon  enter- 
ing the  cavities  formed  to  replace  the  dissolved  lime. 

(2)  DEPOSITION.     Quartz  crystals  sometimes  form  on 
the  mineral   Fluorite  by  the  deposit  of  a  silicious  solution 
and  the  mineral  Anglesite  forms  on  Cerussite  by  incrustation. 

(3)  ALTERATION.     This   is   the   most   common   change 
in  minerals,  and  the  most  active  agents  are  the  gases.    Thus 
Azurite  giving  up  its  oxygen,  water  and  carbonic  acid,  forms 
native  copper,  by  loss  of  some  of  its  constituents.    The  min- 


MINERALOGY  121 


eral  Brochantite,  giving  up  its  sulphur  and  water  forms 
Cuprite, — a  copper  oxide,  which  in  turn  taking  up  carbonic 
acid  is  changed  to  Malachite,  a  copper  carbonate.  Pyrite 
giving  up  its  sulphur  and  taking  on  oxygen  forms  the  min- 
eral Limonite. 

Internal  Imperfections  and  Inclusions 

41.  A  mineral  in  crystallizing  sometimes  includes  an  air 
bubble,  a  liquid  globule  or  organic  matter  like  Bitumen,  etc., 
so  that  it  results  in  an  imperfectly  crystallized  mineral,  and 
these  things  result  in  that  infinite  variety  which  perplex  the 
mineralogists  and  often  render  chemical  analysis  necessary  to 
correctly  classify  a  mineral. 

Other  Simple  Mineral  Tests 

42.  The  physical  properties  already  explained  -do  not 
involve  any  physical  or  chemical  change  in  the  composition 
or  structure  of  a  mineral.     There  are  two  simple  tests  on 
minerals   that   involve   changes   both   physical   and   chemical 
which  may  with  propriety  be  considered  under  the  subject 
Mineralogy,  as  follows: 

FUSIBILITY 

When  a  mineral  can  be  melted  simply  by  the  application 
of  heat  it  is  said  to  be  fusible;  however,  if  Fluxes  (Chemical 
Reagents)  are  necessary  to  fuse  a  mineral,  it  is  said  to  be 
infusible.  In  order  to  determine  the  fusibility  of  a  mineral, 
and  the  ease  or  difficulty  with  which  this  may  be  accom- 
plished, mineralogists  have  adopted  a  scale,  beginning  with 
unity  1,  representing  the  most  fusible  mineral,  and  advancing 


122     PRACTICAL  GEOLOGY  AND  MINERALOGY 

to  6,  the  most  difficultly  fusible  mineral.  Anything  above  6 
in  the  scale  is  said  to  be  infusible.  The  following  is  the  scale 
and  the  typical  minerals  used  by  way  of  comparison,  viz  :— 

FUSIBILITY  SCALE 

(1)  STIBNITE      (Antimony).     Most     fusible     mineral 
known;  melts  in  large  pieces  in  ordinary  candle  flame.     A 
lighted  match  will  fuse  small  splinters  of  Stibnite. 

(2)  NATROLITE    (Natron    Soda).     Fusible    in    candle 
flame  in  small  splinters,  but  more  difficult  than  Stibnite. 

(3)  RED  GARNET  (Almondlte).     Fusible  in  Blow  Pipe 
flame,    but    withstands   candle    flame    even    in    the    smallest 
splinters. 

(4)  ACTINOLITE.     Easily  fusible  in  Blowpipe  flame  in 
small  pieces,  but  large  pieces  fuse  only  with  difficulty. 

(5)  ORTHOCLASE   (Feldspar).     Fusible     in     Blowpipe 
flame  in  small  pieces,  large  pieces  will  not  melt. 

(6)  BRONZITE  (Serpentine).  Almost  infusible  in  Blow- 
pipe flame.    Very  fine  splinters  are  slightly  rounded  on  edgec, 
but  require  a  lens  to  detect  any  change. 

(7)  QUARTZ.    Infusible  in  Blow  Pipe  flame  even  on  the 
thinnest  edges. 

In  the  examination  of  a  mineral  specimen  as  to  fusibility, 
it  is  tested  in  candle  flame  and  if  found  infusible  by  this 
method  then  the  Fusibility  is  above  2,  and  Blow  Pipe  must 
be  used.  A  splinter  of  the  mineral  to  be  tested  should  be 
held  in  a  forceps,  ground  to  a  thin  point,  so  as  not  to  con- 
duct away  too  much  heat. 


MINERALOGY 


123 


TABLE  OF  FUSIBILITY  OF  COMMON   MINERALS  ' 

No.    1 

Sylvanite 

Calavarite 

Hessite 

Livingstonite 

Proustite 

Stephenite 

Cerargyrite 

Embolite 

Jamesonite 

Zinkenite 

Mendipite 

Grunauite 

Cinnabar 

Coloradoite 

Epsomite 

Orpiment 

Realgar 

Krennerite 

NO.  \y2 

Petzite 

Nagyagite 

Sylvite 

Pyrargyrite 

Tetrahedrite 

Valentinite 

Vanadinite 

Cerussite 

Argentite 

Halite 

Borax 

Tetradimite 

No.    2 

Chalcopyrite 

Galena 

Wulfenite 

Niccolite 

Breithauptite 

Arsenopyrite 

No.  2y2 

Chalcocite 

Smaltite 

Anglesite 

Olivenite 

Covelite 

Bornite 

No.  3 

Atacamite 

Cuprite 

Stolzite 

Malachite 

Azurite 

Wolframite 

Cobaltite 

Pyrrhotite 

Gypsum 

Boracite 

Fluorite 

Atacamite 

Witherite 

Melaconite 

No.  4 

Barite 

Celestite 

Pyroxine 

Amphibole 

Hornblende 

Labradorite 

Andesite 

Titanite 

Hubnerite 

No.  5 

Sphalerite 

Smithsonite 

Willemite 

Calamine 

Leucopvrite 

Siderite 

Apatite 

Beryl 

Muscovite 

Biotite 

Talc 

Scheelite 

124     PRACTICAL  GEOLOGY  AND  MINERALOGY 


No.  6 

Dioptase  Genthite  Limonite 

Franklinite  Chromite  Rutile 

Magnetite  Cassiterite  Topaz 

Pyrolusite  Corundrum  Alunogen 

Uranite  Spinel  Crysocolla 

Amethyst  Magnesite  Hematite 

Turquoise  Zincite  Gummite 

INFUSIBLES 

Rhodochrosite,  Diamond,  Quartz,  Asbetos,  Cyanite, 
Topaz,  Agate,  Jasper,  Opal. 

Acid  Mineral  Tests 

43.  A  simple  test  to  determine  a  carbonate  mineral  is 
to  drop  a  little  acid  on  the  mineral ;  if  it  is  a  carbonate,  it  will 
cause  an  effervescence  (fizzing)  due  to  the  carbonic  acid  set 
free.  Limestone  effervesces  most  freely.  A  more  satis- 
factory test  for  one  of  the  common  mineral  carbonates  is  to 
pulverize  the  mineral  and  place  the  pulp  in  a  glass  or  por- 
celain vessel  and  then  apply  the  acid.  In  the  absence  of 
Nitric,  Hydrochloric  or  Sulphuric  acids,  a  good  quality  of 
vinegar,  which  is  a  diluted  fruit  acid,  will  give  fair  results. 

Particles  of  free  gold  in  a  mineral  may  be  tested  by 
dropping  a  little  acid  on  it;  if  the  metallic  particles  remain 
unchanged  in  luster,  etc.,  then  you  may  be  reasonably  certain 
it  is  gold.  Pyrites  are  only  slightly  affected  by  acids,  but  a 
change  in  luster  is  always  noticeable  which  serves  to  dis- 
tinguish them  from  gold. 


MINERALOGY  125 


CHEMICAL  PROPERTIES  OF  MINERALS 

44.  The  determination  of  a  pure  mineral  by  its  physical 
properties    is    not    difficult,    but    complex    minerals    require 
careful  and  persistent  examination  to  make  an  accurate  deter- 
mination of  their  identity.     The  final  and  conclusive  test  on 
a  mineralogical  specimen  is  a  chemical  analysis,  which  sub- 
ject is  outside  the  purview  of  this  book. 

It  must,  however,  be  borne  in  mind  that  the  chief 
distinction  between  a  mineral  and  a  rock  is  in  their  chemical 
composition.  A  rock  is  an  aggregate  of  minerals,  a  mere 
mixture,  while  a  mineral  has  a  definite  and  fixed  proportion 
of  elements  in  its  composition.  If  the  identity  of  a  certain 
mineral  is  established  by  physical  properties  heretofore 
named,  a  chemical  determination  or  assay  is  unnecessary, 
because  the  composition  of  every  pure  mineral  is  known  and 
its  percentage  of  elements  shown  in  mineralogical  tables. 
For  example:  If  we  test  a  mineral  and  find  it  has  all  the 
properties  of  say  Chalcocite,  turn  to  the  mineralogical  table 
for  that  mineral  and  you  will  find  it  is  composed  of  79.8% 
copper  and  20.2% sulphur  and  never  otherwise  if  pure. 
In  ordinary  practice  perfect  minerals  are  rare,  owing  to 
impurities  present.  Supose  the  mineral  is  only  50%  pure, 
then  there  would  be  approximately  40%  copper  and  so  on. 

In  Mineralogical  tables  the  composition  is  usually  given, 
either  in  the  way  of  a  formula  or  expressed  in  percentage, 
calculated  from  the  the  formula,  in  other  words  you  have 
the  answer  at  the  beginning,  whereas  in  actual  practice  this 
would  come  at  the  end  of  the  examination. 

How  to  Examine  and  Determine  Minerals 

45.  In  the  usual  study  of  minerals,   specimens  of  the 
normal  types  which  have  been  determined  by  an  expert,  as 


126     PRACTICAL  GEOLOGY  AND  MINERALOGY 

to  their  physical  and  chemical  properties  are  used  for  the 
reason  that  a  real  object  is  more  interesting  than  a  picture 
or  word  description.  Every  one  engaged  in  the  study  of 
minerals  should  have  at  least  specimens  of  such  minerals  at 
hand  that  he  is  most  interested  in. 

Such  a  collection  may  be  obtained  from  dealers  in  min- 
erals at  reasonable  rates  and  will  be  found  of  great  assistance 
as  the  characteristics  may  be  learned  much  as  we  learn  to 
know  a  person  by  his  distinctive  physical  features.  Then  a 
determined  mineral  may  be  tested  by  each  of  the  physical 
properties,  as  Hardness,  Gravity,  etc.,  which  tends  to  fix 
these  in  the  mind  better  than  is  possible  in  any  other  way. 
It  is,  however,  possible  to  form  an  acquaintance  with  the 
more  common  minerals  from  a  description  alone,  and  this 
plan  will  have  consideration  at  this  time. 

The  minerals  hereafter  described  are  those  usually  found 
in  cabinets  of  High  Schools  and  Schools  of  Mines,  each 
being  a  normal  type  of  the  group  to  which  it  belongs,  and 
should  be  of  particular  interest  to  all  students  of  mining. 
The  physical  properties  are  given  in  the  order  previously 
named. 

DESCRIPTIVE  MINERALOGY 
Gold  (Au)  Minerals 

46.  Gold  is  a  metallic  element,  which  with  one  except- 
ion is  always  in  a  free  or  native  state.  Gold  is  widely  dis- 
tributed and  occurs  in  a  variety  of  rocks,  and  in  sea  water, 
though  in  such  relatively  small  quantities  as  to  be  of  little 
importance.  It  enters  into,  and  is  associated  with  all  classes 
of  mineral  compounds,  but  usually  in  a  state  of  mixture 
only,  the  fine  gold  flakes  and  dust  are  coated  with  sulphur, 
arsenic,  iron,  etc.,  so  that  the  gold  is  invisible  even  with  a 


MINERALOGY  127 


magnifying  glass.  Such  mineral  compounds  are  said  to  be 
refractory  although  the  Gold  content  is  thought  to  be  actu- 
ally free. 

In  the  early  days  of  mining,  Gold  was  thought  to  exist 
only  in  quartz  (except  in  placers)  and  this  mineral  is  its 
natural  home.  Iron  and  quartz  have  a  strong  affinity  for 
Gold,  so  sections  of  quartz  veins  that  contain  the  most  iron 
are  generally  the  richest. 

The  only  recognized  chemical  combination  of  Gold  with 
another  element  is  in  the  Tellurides,  where  gold  and  Tellur- 
ium are  in  a  real  chemical  composition,  with  fixed  proportion 
for  each. 

Gold  Telluride  Minerals 

47.  SYLVANITE.  Composition,  Au  28.5%,  Te  55.8%, 
Ag  15.7%.  Luster,  metallic;  Color, 
steel-gray,  silver  white  to  brass-yellow;  Hardness,  1.5  to  2; 
Streak,  gray;  Cleavage,  uneven;  Tenacity,  sectile;  Crystals, 
triclinic,  resembling  Hebrew  written  characters,  hence  some- 
times called  Graphic  Tellurium.  Fusibility  1. 

CALAVARITE.     Composition,  Au  44.5%,  Te  55.5%.     Lus- 
ter, metallic;  Color  and  Streak,  gray  to 
bronze-yellow;    Hardness,    2.5;     Gravity,     9.4 ;    Fracture, 
uneven;  Tenacity,  sectile;  Crystals,  triclinic;  Fusibility,    1. 

NAGYAGITE.     Composition,  Au,   Pb,   Sb,  Te,   S,  somewhat 
variable.      Luster,   metallic;    Color    and 
Streak,   blackish-gray;   Hardness,    1    to    1.5;  Tenacity,   foli- 
ated; Crystals,  orthorhombic ;  Fusibility,   1.5. 

PETZITE.     Composition,     Au     25.6%,     Ag    41.85%,    Te, 

32.68%.     Luster,  metallic;  Color,  iron-gray; 

Streak,  grayish ;  Hardness,  2.5  to  3 ;  Gravity,  8  to  9 ;  Frac- 


128     PRACTICAL  GEOLOGY  AND  MINERALOGY 

ture,  uneven;  Tenacity,  sectile  to  brittle;  Crystals,  massive; 
Fusibility,  1.5. 

KRENNERITE.     Composition,    Au,    Te.      Luster,    metallic; 
Color,      silver- white      to      brass-yellow; 
Streak,  gray ;  Hardness,  2.5 ;  Gravity,  8.35 ;  Cleavage,  basal ; 
Crystals,   orthorhombic ;   Fusibility,    1. 

Remarks:  The  Telluride  minerals  are  among  the  heav- 
iest known  and  this  alone  will  serve  to  identify  them.  When 
Tellurium  appears  in  an  ore  it  indicates  increased  metal 
values. 

Silver   (Ag)   Minerals 

48.  Silver  is  found  native  in  bulk  and  also  in  crystal 
form.  It  enters  into  combinations  with  a  variety  of  elements 
to  form  valuable  minerals.  Silver  is  also  found  in  a  state 
of  alloy  writh  gold  in  ores  verying  from  5  to  35%  silver. 
Silver  occurring  in  quartz  with  gold  is  usually  free-milling. 
Silver  minerals  that  contain  lead  and  copper  sulphides  are 
called  Smelting  Ores.  Those  containing  antimony,  arsenic, 
sulphur  and  zinc  are  termed  Refractory  Ores.  The  Silver 
minerals  constitute  a  large  group,  so  only  the  more  common 
are  described  below,  viz: 

Silver  Glance 

ARGENTITE  (Silver  Glance).  Composition,  Ag  87.1%,  S 
12.9%.  Luster,  metallic;  Color  and  Streak, 
blackish  to  lead-gray;  Hardness,  2  to  2.5;  Gravity,  7.6; 
Fracture,  conchoidal;  Tenacity,  very  sectile;  Crystals,  iso- 
metric; Fusibility,  1.5. 

STROM EYERITE.     Composition,   Ag   53.1%;   Cu   31.2%,    S 

15.7%.       Luster,     metallic;     Color     and 

Streak,   dark-gray;   Hardness,    2.5    to    3;    Gravity,   6.25; 


MINERALOGY  129 


Fracture,  uneven;  Tenacity,  sectile;  Crystals,  orthorhombic ; 
Fusibility,  1.5. 

HESSITE.     Composition,   Ag  62.8%,   Te   37.2%.     Luster, 
metallic;    Color    and    Streak,    grayish;    Hardness, 
2.5  to  3;  Gravity,  8.4;  Fracture,  uneven;  Tenacity,  sectile; 
Crystals,  isometric;  Fusibility,  1. 

PYRARGYRITE  (Ruby  Silver).  Composition,  Ag  59.8,  Sb 
22.5%,  S  17.7%.  Luster,  metallic  to  ada- 
mantine ;  Color  and  Streak,  black  to  dark-red ;  Hardness, 
1.5  to  2;  Gravity,  5,8;  Fracture,  conchoidal;  Crystals,  hex- 
agonal; Cleavage,  imperfect;  Fusibility,  1. 

PROUSTITE  (Light  Ruby  Silver).  Composition,  Ag  65.5%, 
As  15.1%,  S  16.2%;  Sb.  Luster,  splendant  to 
adamantine;  Color,  light  ruby-red;  Streak,  scarlet-red; 
Hardness,  2  to  2.5 ;  Gravity,  5.5 ;  Fracture,  conchoidal ; 
Tenacity,  sectile  to  brittle;  Crystals,  hexagonal;  Fusibil- 
ity, 1. 

STEPHENITE  (Brittle  Silver).  Composition,  Ag  68.5%, 
As  15.1%,  S  16.2%,  (Sb).  Luster,  sub- 
metallic;  Color  and  Streak,  iron-black;  Hardness,  2  to  2.5; 
Gravity,  6.25 ;  Fracture,  uneven ;  Tenacity,  sectile  to  brittle  ; 
Crystals,  orthorhombic;  Fusibility,  1. 

POLYBASITE.     Composition,    Ag   64%,    As,    Cu.      Luster, 
metallic;  Color  and  Streak,  black;  Hardness, 
2  to  2.5;  Gravity,  6.2;  Fracture,  uneven;  Tenacity,  sectile 
to  brittle;  Crystals,  monoclinic;  Fusibility,  1. 

CERARGYRITE   (Horn  Silver).     Composition,  Ag  75%,  Cl 

24.6%.       Luster,     resinous     to     wax-like; 

Color,  green,  gray  to  blue;  Streak,  shining;  Hardness,  1.5 

to  2;  Gravity,   5.4;  Fracture,  uneven,  compact;  Tenacity, 


130        PRACTICAL  GEOLOGY  AND  MINERALOGY 

malleable;  Crystals,  rare,  isometric  in  small  cubes;  Fusibil- 
ity, 1. 

Remarks:  When  this  mineral  occurs  massive  it  appears 
horn-like,  hence  its  name,  which  does  not  refer  to  its  ap- 
pearance in  the  "horn-spoon,"  as  some  think. 

IODYRITE.     Composition,  Ag  46%,   1.54%.     Luster,  resin- 
ous to  waxy;  Color  and  Streak,  yellow;  Frac- 
ture, uneven;  Cleavage,  basal;  Gravity,  5.6;  Tenacity,  sec- 
tile  to  malleable ;  Crystals,  hexagonal ;  Fusibility,  1 . 

EMBOLITE.     Composition,   Ag,   Cl,   Br.     Luster,   resinous; 
Color,  olive-green  to  yellowish;   Streak,  shin- 
ing; Hardness,  1  to  1.5;  Gravity,  5.5;  Crystals,  isometric; 
Fusibility,  1. 

BROMYRITE.  Composition,  Ag  57.4%,  Br  42.6%.  Luster, 
adamantine;  Color,  greenish,  bluish  to  yel- 
low; Streak,  yellowish-green;  Hardness,  2  to  3 ;  Gravity, 
5.9;  Fracture,  uneven;  Tenacity,  malleable;  Crystals,  iso- 
metric; Fusibility,  1. 

Copper   (Cu)   Minerals 

49.  COPPER  (Cu)  is  an  element  that  frequently  occurs 
free  as  a  result  of  nature's  processes.  It  crystallizes  in  the 
isometric  system  in  more  or  less  distorted  cubes.  It  also 
occurs  native  in  the  shape  of  fine  grains,  most  noticeably  in 
the  region  of  Lake  Superior.  Copper  combines  freely  with 
various  elements  to  form  compounds  which  minerals  are  the 
chief  source  of  the  commercial  metal.  The  Copper  minerals 
of  most  importance  are  the  following : 

CUPRITE    (Ruby  Copper  Ore).     Composition,  Cu  88.8%, 

O,  21.1%.     Luster,  adamantine  to  earthy;  Color 

and  Streak,  deep-red  to  brownish-red ;  Hardness,  3.5 ;  Grav- 


MINERALOGY  131 


ity,  6  to  6.5;  Fracture,  uneven,  compact;  Tenacity,  brittle; 
Crystals,  isometric  in  ideal  cubes;  Fusibility,  2.5  to  3. 

MELACONITE  (Black  Copper  Ore).  Composition,  Cu 
78.9%,  O,  21%.  Luster,  sub-metallic; 
Color  and  Streak,  grayish-black;  Hardness,  3  to  4;  Gravity, 
6;  Fracture,  uneven;  Tenacity,  brittle  to  earthy;  Crystals, 
monoclinic;  Fusibility,  3. 

Remarks:  Ores  of  Melaconite  frequently  contain 
earthy  impurities  such  as  sulphur,  iron,  arsenic  and  mangan- 
ese. 

CHALCOPYRITE  (Copper  Pyrites).  Composition,  Cu 
34.6%,  Fe  30.5%,  S  34.9%.  Luster, 
shining;  Color,  brass-yellow  to  deep  yellow;  Streak,  green- 
ish-black; Hardness,  3.5  to  4;  Gravity,  4.3;  Fracture, 
uneven;  Tenacity,  sectile  to  brittle;  Crystals,  tetragonal; 
Fusibility,  2. 

Remarks:  This  mineral  occurs  in  various  rocks,  fre- 
quently associated  with  galena  and  with  other  copper  ores. 


CHALCOCITE   (Copper  Glance).     Composition,  Cu  79.J 

S  20.2%.  Luster,  shining;  metallic;  Color 
and  Streak,  blackish-lead-gray;  Hardness,  2.5  to  3;  Gravity, 
5.5;  Fracture,  uneven;  Tenacity,  knife  cuts  it;  Crystals, 
orthorhombic ;  Fusibility,  2  to  2.5. 

Remarks:    Chalcocite  closely  resembles  Argentite  (silver 
Sulphide)    but  is  not  sect-ile. 

BORNITE  (Peacock  Copper).  Composition,  Cu  55.5%, 
Fe  16.3%,  S  28.6%.  Luster,  metallic;  Color, 
blue  to  copper  red;  Streak,  grayish-black;  Fracture,  uneven; 
Hardness,  3;  Gravity,  4.5  to  5;  Tenacity,  sectile  to  brittle; 
Crystals,  isometric;  Fusibility,  2.5. 


132     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Remarks:  Bornite  is  distinguished  from  Chalcopyrite 
by  its  bronze-red  to  copper-red  color  on  fresh  fractured 
surfaces. 

TETRAHEDRITE  (Gray  Copper).  Composition,  Cu  25.5%, 
S,  As,  Ag,  Hg.  Luster,  metallic;  Color, 
steel-gray  to  blackish-gray;  Streak,  brown  to  cherry-red; 
Hardness,  3  to  4.5;  Gravity,  4.7  to  5.6;  Fracture,  uneven; 
Tenacity,  brittle;  Crystals,  isometric;  small  but  perfect; 
Fusibility,  1.5  to  2. 

MALACHITE  (Green  Copper  Carbonate).  Composition, 
Cu  71.9%,  C  19.9%,  O.  Luster,  adaman- 
tine to  vitreous ;  Color,  light-green ;  Streak,  pale-green ; 
Hardness,  3.5  to  4;  Gravity,  3.7  to  4;  Fracture,  uneven  to 
Fibrous;  Tenacity,  brittle;  Crystals,  monoclinic;  Fusibil- 
ity, 3. 

Remarks:  This  mineral  is  a  common  outcrop  of  copper 
veins  and  when  hard  and  solid  takes  a  fine  polish  as  an 
ornamental  stone. 

AZURITE  (Blue  Copper  Carbonate).  Composition,  Cu 
69.2%,  C  25.6%,  O.  Luster,  vitreous  to  trans- 
parent ;  Color  deep  azure-blue ;  Streak,  bluish ;  Hardness, 
3.5  to  4.5;  Gravity,  3.5  to  3.8;  Fracture,  conchoidal  or 
uneven ;  Tenacity,  brittle ;  Crystals,  monoclinic ;  Fusibility,  3. 

Remarks:  Azurite  occurs  with  Malachite  at  copper 
outcrop,  giving  a  stain  to  associated  rocks. 

CHRYSOCOLLA  (Copper  Silicate).  Composition,  Cu  45.3%, 
Si  34.2%.  Luster,  shining  to  earthy;  Color, 
clear  bluish-green ;  Hardness,  2  to  4 ;  Gravity,  2  to  2.5 ; 
Fracture,  uneven;  Tenacity,  sectile  to  brittle;  Crystals, 
massive,  never  crystallized ;  Fusibility,  6. 


MINERALOGY  133 


Remarks:  Chrysocolla  occurs  in  thin  seams  in  crevices 
as  an  incrustation. 

ATACAMITE   (Copper  Chloride).     Composition,  Cu  58.7% 
Cl    32.8%.      Luster,    adamantine    to    vitreous; 
Hardness,  3  to  3.5;  Fracture,  conchoidal;  Tenacity,  brittle; 
Crystals,  orthorhombic ;  Fusibility,  3  to  4. 

OLIVENITE  (Copper  Arsenide).  Composition,  Cu  56.15%, 
As  40.6.  Luster,  vitreous  to  adamantine; 
Color  and  Streak,  olive-green  to  brown;  Hardness,  3; 
Gravity,  4.25;  Fracture,  uneven;  Tenacity,  brittle-fibrous; 
Crystals,  orthorhombic,  ideal,  symmetry ;  Fusibility,  2  to  2.5. 

Lead  (Pb)  Minerals 

50.  LEAD  (Pb)  is  a  very  common  element,  never 
occurs  native,  but  its  compounds  are  quite  numerous.  The 
lead  minerals  are  all  heavy  and  quite  soft  and  these  proper- 
ties alone  give  a  clue  to  the  class  to  which  they  belong. 
The  following  are  the  principal  Lead  minerals: 

GALENA  (Lead  Glance).  Composition,  Pb  86.6%,  S 
13.4%.  Luster,  metallic,  shining;  Color  and 
Streak,  lead-gray ;  Hardness,  2.5 ;  Gravity,  7.25 ;  Fracture, 
granular;  Cleavage,  cubic;  Crystals,  isometric,  ideal  cubes; 
Fusibility,  2. 

Remarks:  Galena  occurs  in  granite,  limestone  and 
sandstone  and  is  often  associated  with  copper  and  zinc  ores. 
The  ore  matrix  is  quartz,  calcite,  and  fluor-spar.  Galena  is 
the  most  common  as  well  as  the  most  important  lead  ore. 
All  Galena  ores  carry  some  silver,  ranging  from  1  to  10%. 

CERUSITE    (White   Lead   Ore).      Composition,    Pb   83.5% 

C    16.5%.      Luster,,    adamantine;     Color     and 

Streak,  white  to  grayish;  Hardness,  3  to  3.5;  Gravity,  6.5; 


134     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Fracture,    conchoidal;   Tenacity,    brittle;    Crystals,    orthor- 
hombic;  Fusibility,  1.5. 

Remarks:     Cerusite    is   a   valuable   lead    carbonate    ore 
tnd  runs  to  Galena  with  depth. 

JAMESONITE  (Feather  Ore).  Composition,  Pb,  Sb,  S. 
Luster,  sub-metallic;  Color,  blackish  lead- 
gray;  Streak,  black;  Hardness,  2  to  3;  Gravity,  5  to  5.5; 
Fracture,  uneven ;  Tenacity,  brittle ;  Crystals,  orthorhombic ; 
Fusibility,  1. 

ANGLESITE.  Composition,  Pb  64.1%,  O,  24%,  S  14.8%. 
Luster,  adamantine  to  resinous;  Color, 
white-gray  to  green;  Streak,  white  to  gray;  Hardness,  2.5 
to  3;  Gravity,  6.4;  Fracture,  conchoidal;  Tenacity,  brittle; 
Crystals,  orthorhombic;  Fusibility,  2.5. 

Remarks:     Anglesite    is    an    important    Lead    ore    and 
occurs  in  the  Oxide  Zone,  running  to  Galena  with  depth. 

PYROMORPHITE.  Composition,  Pb,  As,  O,  Cl.  Luster, 
resinous,  sub-transparent;  Color,  green, 
brown,  yellow  to  gray;  Streak,  white;  Hardness,  3.5  to  4; 
Gravity,  7;  Fracture,  uneven;  Tenacity,  brittle;  Crystals, 
hexagonal  prisms;  Fusibility,  2. 

Remarks:     Occurs  in  veins  with  other  lead  ores. 

MIMETITE.  Composition,  Pb,  As,  O,  Cl.  Luster,  resin- 
ous to  adamantine;  Color,  pale  brownish- 
yellow  ;  Streak,  white  to  gray ;  Hardness,  2.5  to  3.5 ; 
Gravity,  6.4;  Fracture,  uneven;  Tenacity,  brittle;  Crystals, 
hexagonal;  Fusibility,  1.5. 

Zinc  (Zn)  Minerals 

61.     ZINC    (Zn)    is  an  element  said   to   occur   native 
only  in  Australia,   and   this   is  somewhat   doubtful.     The 


MINERALOGY  135 


compounds  of  Zinc  are  quite  numerous;  when  it  occurs  in 
the  ores  of  other  metals  it  makes  them  refractory  and  sub- 
ject to  penalties  at  the  smelters  according  to  the  Zinc 
content.  Zinc  is  the  most  difficultly  fusible  of  all  metallic 
ores.  The  following  are  the  principal  Zinc  minerals: — 

SPHALERITE  (Zinc  Blende).  Composition,  Zn  67%,  S 
33%.  Luster,  resinous  to  waxy;  sub-metallic; 
Colors,  various,  from  brownish-yellow,  black,  green,  red  and 
white;  Streak,  white  to  reddish-brown;  Fracture,  conchoid- 
al;  Tenacity,  brittle;  Hardness,  3.5  to  4;  Gravity,  4; 
Crystals,  isometric  modified  cubes;  Fusibility,  5. 

Remarks:  Sphalerite  is  called  "Black-jack"  by  the 
miners.  It  is  the  most  common  and  valuable  Zinc  ore  of 
commerce  and  occurs  frequently  in  sulphide  copper  and  lead 
ores.  Zinc  ores  carry  gold  and  silver  at  times  but  in  too 
small  proportions  to  be  extracted  with  profit  except  as  a 
by-product  in  Zinc  smelting. 

SMITHSONITE  (Zinc  Carbonate).  Composition,  Zn  52%, 
C  9.76%,  O  38.24%.  Luster,  vitreous  or 
pearly;  Color,  whitish-green  to  brown;  Streak,  uncolored; 
Hardness,  5 ;  Gravity,  4.4 ;  Fracture,  uneven ;  Tenacity, 
brittle ;  Fusibility,  5 ;  Crystals,  rhombohedral. 

Remarks:  The  massive  mineral  is  called  "dry-bone" 
by  miners  from  its  characteristic  appearance.  Smithsonite 
is  an  important  Zinc  ore,  nearly  always  associated  with 
silicates. 

CALAMITE    (Zinc   Silicate).      Composition,    Zn    67.5,     Si 
25%.     Luster,  vitreous  to  pearly;  Color,  whit- 
ish, bluish-green  to  brown;  Streak,  white;  Hardness,  4.5  to 


136     PRACTICAL  GEOLOGY  AND  MINERALOGY 

5;   Gravity,   3.25;   Fracture,    uneven;    Tenacity,    brittle; 
Crystals,  orthorhombic ;  Fusibility,  5. 

Remarks:  Calamine  occurs  associated  with  other  Zinc 
ores. 

ZINCITE  (Red  Zinc  Ore).  Composition,  Zn  80.3%,  O 
19.7%.  Luster,  brilliant  to  adamantine;  Color, 
bright  red  to  yellow ;  Streak,  orange-red ;  Hardness,  4  to  4.5 ; 
Gravity,  5.7 ;  Fracture,  mica-like ;  Cleavage,  perfect ;  Ten- 
acity, lamina,  brittle;  Crystals,  hexagonal — well  defined; 
Fusibility,  6. 

Remarks:  Zincite  occurs  with  other  Zinc  ores,  espec- 
ially Franklinite  and  Willemite. 

FRANKLINITE  (Black  Zinc  Ore).  Composition,  Zn,  Fe, 
Mn,  etc.  Luster,  sub-metallic;  Color,  iron- 
black;  Streak,  dark  reddish-brown;  Hardness,  5.5  to  6.5; 
Gravity,  4.5  to  5;  Cleavage,  indistinct;  Tenacity,  brittle; 
Crystals,  isometric;  Fusibility,  6. 

Remarks:  Usually  occurs  in  coarse  grains,  resembling 
Magnetite  and  is  associated  with  Calcite,  Zincite  and  Wil- 
lemite. 

WILLEMITE  (Zinc  Silicate).  Composition,  Zn,  O,  Si. 
Luster,  vitreous,  transparent  to  opaque;  Color, 
whitish-green;  Streak,  uncolored;  Hardness,  5.5;  Gravity, 
4;  Fracture,  uneven;  Tenacity,  brittle;  Crystals,  rhombo- 
hedral;  Fusibility,  5. 

Remarks:  Willemite  occurs  with  Franklinite  and  Zinc- 
ite, so  as  to  make  it  an  important  Zinc  ore. 

Cobalt  (Co)  Minerals 

52.  COBALT  (Co)  is  an  element  never  found  native, 
but  combines  with  Sulphur,  Arsenic  and  Antimony  to  form 


MINERALOGY  137 


several  compounds.  Cobalt  is  usually  associated  with  Nick- 
el and  has  recently  attracted  attention  on  account  of  the 
Silver  found  associated  with  it  in  Canadian  ores.  It  is 
highly  magnetic  like  Nickel,  but  retains  its  magnetism  per- 
manently. The  principal  Cobalt  minerals  are  the  follow- 
ing:— 

SMALTITE  (Cobalt  Arsenide).  Composition,  Co  25%,  Ni, 
As.  Luster,  metallic;  Color,  tin-white  to  steel- 
gray;  Streak,  grayish-black ;  Hardness,  5.5  to  6;  Gravity, 
6.5 ;  Fracture,  uneven ;  Cleavage,  cubic ;  Tenacity,  brittle ; 
Crystals,  isometric;  Fusibility,  2.5. 

COBALITE  (Cobalt  Glance).  Composition,  Co  35.5%, 
As  45.2,  S  19.3%.  Luster,  metallic;  Color, 
silver-white;  Streak,  grayish-black;  Hardness,  5.5;  Gravity, 
6.3;  Fracture,  uneven;  Cleavage,  cubic;  Tenacity,  brittle; 
Crystals,  isometric;  Fusibility,  2  to  3. 

ASBOLITE  (Cobalt  Oxide).     Composition,  Co  and  O  24%, 
Mn  and  O  76%.     Luster,  dull  to  sub-metallic; 
Color,    blue    to    blue-black;    Tenacity,     earthy;     Crystals, 
massive. 

Nickel  (Ni)  Minerals 

53.  NICKEL  (Ni)  is  an  element  found  in  native  state 
only  in  meteoric  iron.  It  combines  with  other  elements  to 
form  a  small  group  of  compounds.  Nickel  is  magnetic,  but 
loses  its  magnetism  when  heated  and  this  fact  assists  in  its 
determination.  Nickel  minerals  are  not  widely  distributed, 
but  where  they  occur  they  are  quite  valuable.  The  follow- 
ing are  the  principal  Nickel  minerals: — 
GARNIERITE  (Nickel  Silicate).  Composition,  Ni,  Mg,  O, 
Si.  Luster,  resinous  to  earthy;  Color,  apple- 
green  ;  Streak,  greenish-white ;  Hardness,  2.5 ;  Gravity,  2.3. 


138    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Remarks:  Garnierite  is  never  crystallized,  resembles 
Chrysocolla;  occurs  in  Serpentine  rocks  and  is  of  minor 
importance  as  an  ore. 

MILLERITE  (Nickel  Sulphide).  Composition,  Ni  64.4%, 
S  33.6%.  Luster,  metallic;  Color,  brass- 
yellow;  Streak,  bright;  Hardness,  3  to  3.5;  Gravity,  5.5; 

Fracture,    uneven;    Tenacity,    brittle;    Crystals,    rhombo- 

hedral;  Fusibility,  2. 

NICCOLITE  (Nickel  Arsenide).  Composition,  Ni  44%,  As, 
Sb.  Luster,  metallic ;  Color,  copper-red ; 

Streak,  pale-brown ;  Fracture,  uneven ;  Hardness,  5  to  5.5 ; 

Tenacity,  brittle;  Crystals,  hexagonal;  Fusibility,  2. 

Mercury  (Hg)  Minerals 

54.  MERCURY  (Hg)  is  the  only  element  that  is  a 
liquid  at  ordinary  temperature.  It  forms  alloys  with  several 
metals  but  has  the  greatest  affinity  for  silver  and  gold. 
Mercury  minerals  are  few  and  not  widely  distributed ;  they 
occur  as  a  rule  in  metamorphic  rock.  The  Mercury  minerals 
are  very  heavy,  and  this  permits  working  ores  running  as 
low  as  2%  by  concentration  process.  The  following  are  the 
principal  Mercury  minerals: — 

CINNABAR  (Mercury  Sulphide).  Composition,  Hg  86%, 
S  14%.  Luster,  dull  to  adamantine;  Color, 
bright-red  to  brown ;  Streak,  scarlet-red ;  Hardness,  2  to  2.5  ; 
Gravity,  8  to  9;  Tenacity,  sectile-pulverizes ;  Crystals,  hex- 
agonal; Fusibility,  1;  volatilizes  at  about  1.5. 

COLORADOITE  (Telluride  of  Mercury).  Composition,  Hg, 
Te.  Luster,  metalic;  Color  and  Streak, 
grayish  to  black;  Hardness,  3;  Gravity,  8.6;  Fracture, 
uneven;  Crystals,  rare-massive;  Fusibility,  1;  Volatile  at 
1.5  to  2. 


MINERALOGY  139 


Tin  (Sn)  Minerals 

55.  TIN    (Sn)    occurs  native  in   placers   and   is  then 
called  "Stream  Tin."    It  forms  a  few  compounds  with  other 
elements,  which  are  quite  valuable,   but  of  limited  occur- 
rence.   The  two  principal  Tin  minerals  are : — 

STANNITE  (Tin  Sulphide).  Composition,  Sn  27%,  Cu, 
Fe,  S.  Luster,  metallic;  Color,  steel-gray  to 
iron-black;  Streak,  blackish;  Fracture,  uneven;  Tenacity, 
brittle;  Hardness,  4;  Gravity,  4.5;  Crystals,  tetragonal; 
Fusibility,  5  to  6. 

Remarks:     Stannite  is  also  called  "Tin  Pyrites." 

CASSITERITE  (Tin  Oxide).  Composition,  Sn  78%,  O  22%. 
Luster,  adamantine;  Color,  black,  brown  to 
yellow;  Streak,  pale-gray  to  brown;  Hardness,  6  to  7 ; 
Gravity,  6.4  to  7;  Fracture,  uneven,  granular;  Tenacity, 
brittle;  Crystals,  tetragonal;  Fusibility,  5  to  6. 

Remarks:  This  mineral  is  called  "Tinstone"  by  the 
miners  and  is  the  chief  source  of  the  world's  supply  of  the 
metal. 

Tungsten  (W)  Minerals 

56.  TUNGSTEN    (W.    from   Wolfram)    is   never   free 
and  as  an  element  forms  only  a  few  compounds,  which  are 
valuable  and   now  much   sought   after  owing  to   its   great 
value  in  steel   manufacture.     This  element  was   unknown 
until  within  the  last  century.     The  following  are  the  prin- 
cipal Tungsten  minerals,  viz: — 

WOLFRAMITE    (Tungstate    of    Iron).      Composition,    W 
51.25%,  Mn  15%,  Fe  16%,  O  18%.     Lus- 
ter, shining  to  dull;    Color,    dark    grayish-black;    Streak, 
reddish-brown;    Hardness,    5    to   5.5;   Gravity,    7    to    7.5; 


140     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Fracture,   uneven;  Tenacity,   brittle;   Crystals,   monoclinic; 
Fusibility,  3  to  3.5. 

HUBNERITE  (Tungstate  of  Manganese).  Composition,  W 
61%,  Mn  18%,  O  21%.  Luster,  resinous; 
Color,  brown  to  black;  Streak,  grayish-brown;  Hardness,  5 
to  5.5;  Gravity,  6;  Fracture,  uneven;  Tenacity,  brittle; 
Crystals,  monoclinic;  Fusibility,  7. 

SCHEELITE  (Tungstate  of  Calcium).  Composition,  W 
61%,  Ca  14%,  O  22%.  Luster,  vitreous; 
Color,  white,  yellow-brown,  green;  Streak,  white  to  gray; 
Hardness,  4.5  to  5;  Gravity,  6;  Tenacity,  brittle;  Crystals, 
tetragonal;  Fusibility,  5. 

.Remarks:  Scheelite  occurs  in  California,  Wolframite 
and  Hubnerite  in  Colorado,  Arizona  and  Nevada.  Tung- 
sten ores  to  be  marketable  should  contain  40  to  50%  Tung- 
sten and  be  free  from  sulphur  and  phosphorus.  The  high 
specific  gravity  of  these  minerals  makes  concentration  easy 
so  that  a  60%  concentrate  can  be  produced  from  ores  con- 
taining 5  to  10%  Tungsten. 

Titanium  (Ti)  Minerals 

57.  This  is  a  rare  element  of  recent  discovery.  It 
forms  a  few  compounds  of  importance.  Titanium  (Ti)  is 
used  in  the  manufacture  of  artificial  teeth,  coloring  porcelain 
and  in  certain  alloys  of  iron  and  steel. 

The  principal  Titanium  minerals  are  as  follows: 

RUTILE  (Titanium  Oxide).  Composition,  Ti  61%,  O 
39%.  Luster,  metallic;  Color,  red  to  black; 
Streak,  light-brown;  Hardness,  6  to  6.5;  Gravity,  4.25; 
Fracture,  uneven;  Tenacity,  brittle;  Crystals,  tetragonal; 
Fusibility,  5  to  6. 


MINERALOGY  141 


Remarks:     This  is  the  principal  commercial  mineral. 

TITANITE  (Silicate  of  Titanium).  Composition,  Ti,  O 
40.83%,  Si  30.6%,  Ca  23%.  Luster,  adamantine 
to  reisinous;  Color,  grayish-brown  to  black;  Streak,  uncol- 
ored ;  Fracture,  uneven ;  Cleavage,  prismatic ;  Tenacity,  brit- 
tle; Crystals,  monoclinic;  Hardness,  5  to  5.5;  Gravity,  3.5; 
Fusibility,  4. 

Vanadium  (V)  Minerals 

58.  VANADIUM    (V)    is  a  rare  element  of  recent  dis- 
covery; it  forms  a  few  compounds  with  other  elements  of 
value.    Vanadium  is  used  in  the  manufacture  of  steel,  giving 
it  uniformity  of  structure,  prevents  crystallization,  and  in- 
creases the  tensile  strength  of  steel  when  0.1%  or  less  is 
used  in  an  alloy.    The  following  are  the  principal  Vanadium 
minerals : — 

VANADINITE.  Composition,  V,  Pb,  O,  Cl.  Luster,  res- 
inous to  greasy;  Color,  yellow,  red  to 
brown ;  Streak,  light-yellow ;  Hardness,  2.5  to  3  ;  Gravity,  7 ; 
Fracture,  uneven;  Tenacity,  brittle;  Crystals,  hexagonal; 
Fusibility,  1.5. 

Remarks:  Vanadinate  is  sometimes  classed  a  Lead 
mineral.  Vanadium  is  also  associated  with  the  element 
Uranium. 

Uranium   (U)   Minerals 

59.  URANIUM  (U)  is  an  element  that  has  been  known 
to   mineralogists    for   some   years   but   has   recently   excited 
interest  from  the  fact  that  Radium  (Ra),  a  very  rare  element 
and    almost   priceless    in    value,    has    been    extracted    from 
Uranium  minerals.    The  principal  are  the  following : — 


142     PRACTICAL  GEOLOGY  AND  MINERALOGY 

URANINITE    (Pitch  Blende).     Composition,   U   81.5%,  O 
13.47%,    Pb   3.97%.      Luster,   sub-metallic   or 
dull;  Color,   grayish,   brownish   to  velvet-black;   Hardness, 
5.5;  Gravity,  6.4  to  9.3;  Fracture,  uneven;  Tenacity,  brit- 
tle; Crysetals,  isometric;  Fusibility,  6. 
CARNOTITE.    Composition,  U,  V,  K,  O,  etc.    Color,  bright 
canary-red;    Scale-like;    Crystals,    microscopic. 
Highly  radio-active. 

Molybdenum  (Mo)  Minerals 

60.  MOLYBDENUM  (Mo)  is  a  somewhat  rare  element, 
and  forms  few  compounds.     It  is  one  of  the  steel  hardening 
elements  which  is  growing  in  importance.     It  imparts  to 
steel  properties  similar  to  Tungsten.     The  process  of  treat- 
ment  to   recover   Molybdenum   from   an  ore   is  expensive, 
hence  only  high  grade  minerals  are  of  importance.    The  fol- 
lowing are  the  principal  Molybdenum  minerals: — 
MOLYBDENITE  (Molybdenum  Sulphide).  Composition,  Mo 

59%,  S  41%;  Color  and  Streak,  lead-gray; 
Luster,  metallic;  Hardness,  1  to  1.5;  Gravity,  4.5;  Cleav- 
age, foliated  like  Graphite;  Tenacity,  sectile;  Crystals, 
hexagonal;  Fusibility,  6. 

WULFENITE  (Lead  Molybdate).  Composition,  Mo  35%, 
Pb  65%.  Luster,  vitreous  to  resinous;  Color, 
yellow  to  grayish;  Streak,  gray;  Hardness,  5;  Gravity,  6; 
Fracture,  uneven;  Tenacity,  brittle;  Crystals,  orthorhombic ; 
Fusibility,  2. 

Remarks:     Wulfenite   is  sometimes   classed   as   a   Lead 
Mineral. 

Bismuth  (Bi)  Minerals 

61.  BISMUTH   (Bi)   is  sometimes  found  native  and  is 
clased  as  a  semi-metal.     It  is  used  largely  as  an  alloy  on 


MINERALOGY  143 


account  of  its  low  melting  point.  Bismuth  forms  a  few  com- 
pounds with  other  elements.  These  minerals  are  often  asso- 
ciated with  gold  and  silver  and  it  is  always  an  indicator  of 
increased  richness  in  an  ore.  The  following  are  the  most 
important  Bismuth  minerals:.  . 

BISMUTHINITE  (Bismuth  Glance).     Composition,  Bi  81%, 
S  19%.  Color  and  Streak,  lead-gray;  Hard- 
ness, 2;  Gravity,  6.4;  Crystals,  orthorhombic. 
BISMUTITE     (Bismuth  Carbonate).     Composition,  Bi  79%, 
O    15%,    C    2%.      Color,    white-greenish    to 
yellowish;  Streak,  greenish-gray;  Hardness,  4;  Gravity,  6.8; 
Crystals,  amorphous;  Tenacity,  earthy. 
TETRADIMITE  (Bismuth  Telluride).    Composition,  Bi  51%, 
Te  49%.     Color,  steel-gray;  Streak,   gray; 
Hardness,  1.5  to  2;  Gravity,  7.6;  Cleavage,  basal;  Tenacity, 
sectile,  soils  paper;  Crystals,  hexagonal;  Fusibility,  1.5. 

Platinum  (Pt)  Minerals 

62.  PLATINUM  (Pt)  is  an  element  that  is  nearly  al- 
ways found  native,  and  is  associated  with  Gold  in  placers. 
Four  other  rare  metals,  Osmium,  Palladium,  Ruthenium  and 
Rhodium  are  frequently  associated  with  platinum  in  a  state 
of  alloy.  All  these  meals  have  a  high  value  owing  to  in- 
creasing demand  and  diminshing  supply.  Present  price  of 
Platinum  is  almost  double  pure  gold.  Most  all  the  Platinum 
of  commerce  is  obtained  from  placers,  where  it  occurs  with 
the  black  sands  somewhat  tarnished  in  color,  but  owing  to  its 
great  weight,  and  its  being  insoluble  in  acids,  enables  any 
one  to  distinguish  it  from  ordinary  black  sand. 

Platinum  ore  has  recently  been  discovered  in  paying 
quantities  in  Nevada;  however,  in  the  form  of  a  mixed 
mineral. 


144     PRACTICAL  GEOLOGY  AND  MINERALOGY 


Platinum   forms  compounds  with  only  a  few  elements. 
The  only  minerals  of  importance  are  the  following : — 
SPERRYLITE.        (Platinum     Arsenide).       Composition,     Pt 
56%,   As   43 %\   Color,    tin-white;    Streak, 
black;  Hardness,  6;  Gravity,  10.6;  Crystals,  isometric. 

Remarks:  This  mineral  is  generally  found  in  basic  rocks 
such  as  granite,  serpentine,  etc. 

IRODOSMINE.     Composition,  Ir,  Os,  Ru,  Pt,  Rd;  Hardness, 
6;    Color,    tin-white    to    steel-gray;    Gravitr 
19.3;  Crystals,   hexagonal,   in  minute  prisms. 

Iron  (Fe)  Minerals 

63.  IRON  (Fe)  is  found  native  only  in  meteors,  but  its 
compounds  are  the  most  numerous  of  all  metal  minerals. 
Iron  enters  into  the  composition  of  all  rocks,  minerals  and 
earths,  etc.,  and  its  presence  is  shown  by  the  characteristic 
colors  of  brown  and  j^ellow,  due  to  oxidization  or  iron. 
Iron  minerals  are  so  abundant,  and  the  market  price  of  the 
metal  so  low,  that  only  the  purest  iron  minerals  are  of 
particular  value. 

Pure  iron  minerals  of  highest  commercial  value  occur  in 
the  Azoic  rocks,  but  some  recent  formations  contain  iron 
deposits  of  interest.  Iron  is  magnetic  and  its  presence  in  an 
ore  can  be  detected  ordinarily  by  its  magnetic  properties 
alone.  The  following  are  the  Iron  minerals  of  commercial 
interest : — 

HEMATITE.  (Oxide  Iron).  Composition,  Fe,  70%,  O 
30%.  Luster,  splendent;  Color,  steel-gray  to 
iron  black;  Streak,  reddish  to  brown;  Hardness,  5.5;  Grav- 
ity, 4.5  to  5 ;  Fracture,  uneven,  scaly  to  fibrous ;  Tenacity, 
brittle;  Crystals,  hexagonal;  Fusibility,  6. 


MINERALOGY  145 


Remarks:  Hematite  is  the  most  common  iron  ore; 
Titanium  and  Manganese  are  common  impurities. 
LIMONITE.  (Brown  Iron  Ore).  Composition,  Fe  60%, 
O  26%.  Luster,  sub-metallic,  dull  to  earthy; 
Color,  brown  to  ochre-yellow;  Streak,  yellowish;  Hardness, 
5  to  5.5;  Gravity,  3.5  to  4;  Fracture,  silky;  Tenacity,  brit- 
tle; Crystals,  massive;  Fusibility,  6. 

Remarks:  Brown  and  yellow  ochre,  are  earthly  varie- 
ties of  limonite.  Bog  Iron  Ore  is  Limonite  in  its  first  stages. 
MAGNETITE.  (Magnetic  Iron  Ore).  Composition,  Fe 
72%,  O  27%.  Luster,  metallic;  Color, 
iron-black ;  Streak,  black ;  Hardness,  5.5 ;  Gravity,  6.5 ; 
Fracture,  uneven;  Tenacity,  brittle;  Crystals,  isometric; 
Fusibility,  6. 

SIDERITE.      (Iron  Carbonate).     Composition,   Fe  62%,  C, 
O.     Luster,  pearly;  Color,  grayish  to  brown; 
Streak,  uncolored ;  Hardness,  3  to  4.5 ;  Gravity,  3.8 ;  Crys- 
tals, hexagonal ;  Fusibility,  4.5  to  5. 

Remarks:  Siderite  is  also  called  Spathic  Iron.  It  occurs 
in  stratified  rocks,  gneiss,  slate,  etc. ;  it  is  distinguished  from 
carbonates  of  lime  and  magnesia  by  its  greater  weight,  and 
its  becoming  magnetic  when  heated. 

PYRITE.  (Iron  Pyrites).  Composition,  Fe  46%,  S  53%. 
Luster,  metallic;  Color,  brass-yellow ;  Streak, 
brownish-black;  Hardness,  6  to  6.5;  Gravity,  5;  Fracture, 
uneven;  Tenacity,  brittle;  Crystals,  isometric  cubes;  Fusi- 
bility, 2.5  to  3. 

Remarks:  Pyrite  has  little  value  commercially  for  its 
iron  content,  but  its  sulphur  constituent  is  valuable  for  the 
manufacture  of  Sulphuric  Acid.  Pyrites  are  important  to 
the  miner  on  account  of  their  frequent  association  with  the 


146    PRACTICAL  GEOLOGY  AND  MINERALOGY 

precious  metals,  especially  Gold.  Pyrite  has  been  called 
"Fool's  Gold,"  and  the  novice  in  mining  is  often  puzzled 
by  it,  but  its  brassy  color,  its  brittleness  and  its  sulphur 
fumes  when  heated,  serve  to  distinguish  it  from  Gold. 

PYRRHOTITE.  (Magnetic  Iron  Pyrites).  Composition,  Fe 
57%;  Ni  3%,  S  40%.  Luster,  metallic; 
Color,  bronze-yellow  to  copper-red ;  Streak,  grayish-black ; 
Hardness,  3.5  to  4.5 ;  Gravity,  4.5 ;  Fracture,  uneven ; 
Tenacity,  brittle;  Crystals,  hexagonal;  Fusibility,  2.5  to  3. 

Remarks:  This  is  an  important  Nickel  ore,  although 
percentage  is  small,  never  to  exceed  6%.  Pyrrhotite  is  dis- 
tinguished from  Pyrite  and  Chalcopyrite  by  its  magnetic 
character  and  the  bronze  color  on  a  fresh  fracture.  It  is 
only  about  half  as  hard  as  Pyrite  and  will  not  strike  fire 
with  steel  like  Pyrite.  Hydrochloric  acid  decomposes 
Pyrrhotite,  giving  off  the  odor  of  rotten  eggs. 

Manganese  (Mn)  Minerals 

64.  MANGANESE  (Mn)  occurs  in  combination  with 
other  elements  and  rarely  without  oxygen.  Manganese 
minerals  are  found  in  all  rocks  from  the  Cambrian  to  the 
Tertiary.  Its  principal  use  is  in  the  iron  and  steel  industry. 
A  manganese  ore  to  be  marketable  should  be  free  from 
phosphorus  and  contain  less  than  12%  Silica.  Most  Manga- 
nese ores  carry  Gold  and  Silver  and  are  in  demand  by  the 
Smelters  for  fluxing  and  their  Gold  and  Silver  content  is 
recovered  as  a  by-product.  The  following  are  the  principal 
Manganese  minerals: 

PYROLUSITE.      (Oxide  of  Manganese).     Composition,  Mn 

63%,  O  36%.     Luster,  non-metallic;  Color 

and  Streak,  black;  Hardness,  2  to  2.5;  Gravity,  4.8;  Frac- 


MINERALOGY  147 


ture,    splintery;   Tenacity,    brittle;    Crystals,    orthorhombic ; 
Fusibility,  6. 

Remarks:  Pyrolusite  Is  the  principal  Manganese  ore  of 
commerce. 

RHODOCHROSITE  (Manganese  Carbonate).  Composition, 
Mn  47%,  C  10%,  O  41%.  Luster, 
vitreous;  Color,  rose-red  to  brown*  Hardness,  3.5  to  4.5; 
Gravity,  3.5;  Tenacity,  brittle;  Crystals,  rhombohedral ; 
Infusible,  65. 

Aluminum   (Al)   Minerals 

65.  The  element  ALUMINUM  (Al)  never  occurs  na- 
tive, although  it  is  third  in  abundance  in  the  earth's  crust 
after  Oxygen  and  Silicon.  A  few  years  ago  Aluminum 
metal  was  considered  as  a  chemical  curiosity,  but  it  is  now 
produced  by  electrical  processes  at  a  moderate  cost  and  bids 
fair  to  become  as  common  as  iron  in  the  near  future.  An 
Aluminum  mineral  to  be  commercially  profitable,  should 
contain  40%  or  more  Aluminum  and  be  comparatively  free 
from  impurities.  Aluminum  Oxides  are  9  in  the  scale  of 
hardness  and  include  many  of  the  "Precious  Stones."  The 
Aluminum  minerals  from  which  the  metal  is  extracted  are 
from  2.5  to  5  in  hardness.  The  following  are  the  principal 
Aluminum  metal  minerals,  viz: — 

CRYOLITE.  (Aluminum  Fluoride).  Composition,  Al  13%, 
Fl  54%,  Na  32%.  Luster,  vitreous;  Color 
and  Streak,  white  to  gray ;  Hardness,  2.5 ;  Gravity,  3 ; 
Fracture,  uneven;  Tenacity,  brittle;  Crystals,  monoclinic; 
Fusibility,  1  to  1.5. 

Remarks:  Cryolite  was  the  first  mineral  used  for  ex- 
tracting the  metal,  the  two  elements,  Sodium  and  Fluorine, 


148     PRACTICAL  GEOLOGY  AND  MINERALOGY 

assisting  as  fluxes  in  original  extraction  process,  but  this 
mineral  is  not  much  used  today  on  account  of  its  scarcity  and 
low  percentage  of  Aluminum  content. 

BAUXITE.     (Hydrous  Aluminum  Oxide).     Composition,  Al 
40%,  O  45%.     Luster,  sub-metallic;  Color  and 
Streak,  white  to  brown ;  Hardness,  5  to  5.5 ;  Gravity,  2.5 
to  3.5 ;  Crystals,  orthorhombic. 

Remarks:  Bauxite  is  really  a  Limonite  in  which  the 
iron  has  been  replaced  by  Aluminum.  This  is  the  principal 
source  of  Aluminum  metal  in  the  United  States. 

CORUNDRUM.  (Aluminum  Oxide).  Composition,  Al 
53%,  O  47%.  Luster,  adamantine  to  vit- 
reous, transparent  to  translucent;  Color,  blue,  grayish,  red, 
yellow  to  dark  brown;  Streak,  white  to  gray;  Hardness,  9; 
Gravity,  4.10;  Fracture,  uneven;  Cleavage,  basal;  Tenacity, 
very  tough;  Crystals,  hexagonal;  Fusibility,  6. 

Remarks:  Corundrum  is  not  a  source  of  metal  alumi- 
num, being  too  rare;  it  is  more  valuable  as  an  abrasive,  for 
grinding  and  polishing.  Grinding  stones  are  manufactured 
from  Corundrum  and  when  mixed  with  iron  oxide  forms 
emery  stones.  Natural  Emery  is  found  in  a  few  sections. 
Corundrum  ranks  next  to  the  Diamond  in  hardness,  being  9 
in  the  scale.  There  are  a  number  of  Gem  Stones,  which 
are  simply  varieties  of  colored  Corundrum.  Their  physical 
properties  are  identical  with  Corundrum,  the  only  difference 
is  in  the  color,  as  follows: — 

(a)  Ruby    (Red); 

(b)  Topaz   (Yellow); 

(c)  Sapphire   (Blue)  ; 

(d)  Emerald    (Green)  ; 

(e)  Amethyst   (Violet). 


MINERALOGY  149 


Aluminum  forms  other  compounds,  known  as  Gem 
Stones,  as  follows: 

Spinel.     Composition,  Al  72%,  Mg  28%;  Colors,  red, 
blue,  green,  yellow  to  black. 
CHRYSOBERYL.     Composition,  Al  80.2%,  Glucinium   (Gl) 

19.8%;  Colors,  greenish  to  brown. 

TURQUOISE.    Composition,  Al  46.9%,  P,  O;  Color,  bluish- 
green. 

Calcium  (Ca)   Minerals 

66.  CALCIUM  (Ca)  never  occurs  free,  although  it  is 
one  of  the  most  abundant  elements.  It  forms  a  compound 
with  oxygen  as  Lime  or  Oxide  of  Calcium.  Combined  with 
oxygen  and  carbon  it  forms  Carbonates  as  chalk,  limestone 
and  marble.  Although  Calcium  was  known  to  the  ancients 
the  metal  had  never  been  extracted  until  the  electrical 
process  came  into  use.  Calcium,  combined  with  oxygen 
and  sulphur,  forms  Gypsum,  known  as  Calcium  Sulphate. 
As  a  silicate,  Calcium  occurs  in  a  variety  of  rocks.  The 
following  are  the  principal  Calcium  minerals: — 

CALCITE.  (Calcium  Carbonate).  Composition,  Ca  56%, 
C  &  O  44%.  Luster,  vitreous;  fibrous  to  silky; 
Color,  whitish  to  yellowish ;  Streak,  white  to  gray ;  Hard- 
ness, 3  ;  Gravity,  2.8  ;  Tenacity,  brittle ;  Crystals,  hexagonal ; 
Fusibility,  2.8. 

ARAGONITE.  (Calcium  Carbonate).  Composition,  Ca  56%, 
C  &  O  44%.  Luster,  vitreous  to  transparent ; 
Color  and  Streak,  white  to  gray;  Hardness,  3.5;  Gravity, 
2.9;  Fracture,  uneven;  Tenacity,  brittle;  falls  to  pieces 
with  heat;  Crystals,  orthorhombic ;  Fusibility,  6. 

Remarks:  Calcite  and  Aragonite  are  ideal  minerals  for 
the  manufacture  of  lime,  as  they  contain  few  impurities. 


150     PRACTICAL  GEOLOGY  AND  MINERALOGY 

APATITE.  (Phosphate  of  Calcium).  Composition,  Ca  53%, 
Cl,  P,  O.  Luster,  vitreous;  Color,  greenish  to 
blue,  and  reddish  brown ;  Hardness,  5 ;  Gravity,  3.25 ;  Frac- 
ture, uneven;  Tenacity,  brittle;  Crystals,  hexagonal;  Fusi- 
bility, 6. 

Remarks:  Apatite  or  Lime  Phosphate  is  the  result  of 
animal  matter  accumulations  and  forms  a  valuable  fertilizer 
for  land. 

FLUORITE.  (Calcium  Fluoride).  Composition,  Ca  51%, 
Fl  49%.  Luster,  vitreous  to  adamantine; 
Color,  light  green,  purple,  reddish  and  blue;  Streak,  white 
to  gray;  Hardness,  4;  Gravity,  3;  Fracture,  uneven; 
Tenacity,  brittle;  Crystals,  isometric;  Fusibility,  3. 

Remarks:  Fluorite  is  a  common  veinstone,  in  granites 
and  metamorphic  rocks  and,  when  pure,  is  of  much  value  as 
a  flux;  it  is  used  in  the  manufacture  of  opalescent  glass  and 
in  production  of  Hydrofluoric  Acid,  etc. 

GYPSUM.  (Calcium  Sulphate).  Composition,  Ca  32%, 
S  &  O  46%.  Luster,  vitreous,  or  pearly;  Color, 
white,  yellow  and  brown;  Streak,  white  or  gray;  Hardness, 
1.5  to  2;  Gravity,  2.3;  Cleavage  in  three  directions; 
Tenacity,  brittle  in  opposite  directions;  Flexible;  Crystals, 
monoclinic;  Fusibility,  3  to  3.5. 

DOLOMITE.  (Carbonate  of  Calcium  and  Magnesium). 
Composition,  Ca,  C,  O  54%,  Mg  C,  O  45%. 
Luster,  vitreous  to  pearly;  Colors,  various,  whitish,  yellow- 
ish, brownish  to  black;  Streak,  white  to  gray;  Hardness,  3.5 
to  4 ;  Gravity,  2.8 ;  Tenacity,  brittle ;  Crystals,  hexagonal  ; 
Fusibility,  6. 

Remarks:  This  mineral  is  of  small  importance,  being 
unsuitable  for  lime  burning. 


MINERALOGY  151 


Barium    (Ba)    Minerals 

67.  BARIUM    (Ba)    is  hard  to  separate  from  its  com- 
pounds.     Its  salts  are  used  in  making  fireworks  for  green 
colors;  used  also  in  chemical  work.      Barite  was  formerly 
used  as  an  adulterant  in  white  lead  paints,  and  was  found 
to  stand   weathering   better   than   lead.     There   are  only   a 
few  compounds,  as  follows: — 

BARITE.  (Barytes  or  Heavy  Spar).  Composition,  Ba  65%, 
S,  O  35%.  Luster,  vitreous  to  pearly;  Colors, 
yellowish,  bluish  to  brownish ;  Streak,  white  to  gray ;  Hard- 
ness, 2.5  to  3.5;  Gravity,  4.8;  Fracture,  granular;  Crystals, 
orthorhombic ;  Fusibility,  4. 

Remarks:  Baryte  deceives  many  miners  by  its  weight, 
being  nearly  twice  as  heavy  as  quartz.  It  is  frequently  mis- 
taken for  Scheelite,  but  a  comparison  with  the  properties 
of  Scheelite  will  show  a  distinct  difference,  the  gravity  and 
hardness  of  Scheelite  being  almost  double  that  of  Baryte. 
WITHERITE.  (Barium  Carbonate).  Composition,  Ba  77%, 
C  &  O  23%.  Luster,  resinous;  Color,  yel- 
lowish to  light  gray;  Streak,  gray;  Hardness,  3  to  4;  Grav- 
ity, 4.25 ;  Fracture,  uneven ;  Tenacity,  brittle ;  Crystals, 
orthorhombic;  Fusibility,  2.5  to  3. 

Sodium  (Na)  Minerals 

68.  SODIUM  (Na)  is  one  of  the  most  abundant  elements. 
It  is  found  in  immense  deposits,  combined  with  the  element 
Chlorine,   known  as  Chloride  of  Sodium,  or  common  salt. 
All  sea  water,  as  well  as  the  waters  of  many  springs,  contain 
large  quantities  of  Sodium.     The  principal  Sodium  minerals 
are  as  follows: — 

HALITE.     (Rock  Salt).      Composition,  Na  39%,  Q  61%. 
Luster,  vitreous;  Color  and  Streak,  white  or  gray- 


152     PRACTICAL  GEOLOGY  AND  MINERALOGY 

ish ;  Hardness,  2 ;  Gravity,  2.25 ;  Cleavage,  cubic ;  Tenacity, 
brittle;  Crystals,   isometric. 

NITRATINE.  (Soda  Niter  or  Chili  Saltpeter).  Composi- 
tion, Na  36%,  N  &  O  53%.  Luster,  earthy, 
crusts  and  scales ;  Color,  white,  yellowish  to  grayish ;  Streak, 
white  or  gray ;  Hardness,  1 ;  Fracture,  earthy ;  Tenacity, 
brittle;  Taste,  cooling;  Crystals,  hexagonal. 

Remarks:  Sodium  is  a  constituent  of  many  rocks,  par- 
ticularly in  one  species  of  the  Feldspar  group  known  as 
Plagioclase,  sometimes  called  the  lime-soda  Feldspar.  These 
include  the  minerals,  Albite  (Na  11.8%,  Oligoclase  (Na 
8.8%,  Andesite  (Na  7.7%). 

Potassium  (K)  Minerals 

69.  POTASSIUM  (K  from  Kalium)  occurs  abundantly 
in  nature,  but  always  in  combination  with  other  elements. 
It  exists  in  sea  water,  in  mineral  springs,  in  land  plants, 
and  is  necessary  to  animal  life.  The  most  abundant  source 
of  Potassium  is  the  class  of  Feldspar  known  as  Orthoclase, 
the  other  Potassium  minerals  are  no  doubt  formed  from 
concentrated  solutions  of  Orthoclase,  which  have  become 
crystallized.  The  following  are  the  principal  Potassium 
minerals,  viz: — 

SYLVITE.  (Potassium  Chloride).  Composition,  K  52%, 
Cl  47%.  Luster,  vitreous;  Taste,  salty;  Color 
and  Streak,  white  to  gray;  Hardness,  2;  Gravity,  2;  Frac- 
ture, granular;  perfect  cubes;  Tenacity,  brittle;  Crystals, 
isometric;  Fusibility,  1.5. 

NITER.  (Potassium  Nitrate  or  Saltpeter).  Composition, 
K  39%,  N  14%,  O  47%.  Luster,  earthy;  Hard- 
ness and  Gravity,  2;  Color,  white;  Fracture,  conchoidal ; 
Cleavage,  perfect  prisms ;  Tenacity,  brittle ;  Crystals,  orthor- 
hombic;  Fusibility,  1. 


MINERALOGY  153 


ORTHOCLASE.  (Potash  Feldspar).  Composition,  K  16%, 
Al  18%,  Si  64%.  Luster,  vitreous  to 
pearly;  Color  and  Streak,  white  or  grayish;  Hardness,  6; 
Gravity,  2.5 ;  Cleavage,  basal ;  Crystals,  monoclinic ;  Fusi- 
bility, 5. 

MUSCOVITE.  (Potash  Mica).  Composition,  K  9.2%,  Si 
46%,  Al  46%,  Fe,  Etc.  Luster,  vitreous  to 
pearly;  Color,  white,  green,  yellow  to  brown;  Hardness, 
2  to  2.5 ;  Gravity,  2.8 ;  Cleavage,  basal ;  Tenacity,  tough 
and  elastic. 

Remarks:  Muscovite  is  the  principal  Mica  mineral, 
and  its  value  is  determined  by  the  size  of  the  sheets,  the 
freedom  from  discoloration,  and  its  elasticity.  Its  principal 
use  is  in  electrical  insulations,  glazing,  decorating;  also  used 
in  the  manufacture  of  lubricants. 

Potassium  in  crystals  is  unknown  in  North  America, 
but  the  element  is  found  in  solution,  in  Mono,  Owen's  and 
Searle's  Lakes,  in  the  State  of  California. 

Magnesium    (Mg)    Minerals 

70.  MAGNESIUM  (Mg)  occurs  abundantly,  and  is  a 
constituent  in  many  minerals.  It  has  a  variety  of  uses, 
which  are  increasing  yearly.  It  is  used  in  the  arts  for  flash- 
light powders,  and  also  in  explosives;  the  Sulphate  known 
as  Epsom  Salts,  and  the  powdered  Oxide  have  commercial 
value  as  medicines.  Fireproof  furnace  linings,  and  plaster 
are  made  from  it.  Calcined  Magnesia  is  used  in  paper  manu- 
facture to  give  glossy  surface.  Carbonic  Acid  is  extracted 
from  the  carbonate  for  use  in  soda  water,  etc.  The  prin- 
cipal Magnesium  minerals  are  as  follows: — 
MAGNESITE.  (Magnesian  Carbonite).  Composition,  Mg 
47%,  C  &  O  52%.  Luster,  silky  to  vitreous; 


154     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Color  and  Streak,  white  to  grayish ;  Hardness,  3  to  4.5 ; 
Gravity,  3.3 ;  Cleavage,  rhombohedral ;  Tenacity,  brittle ; 
Crystals,  hexagonal;  Fusibility,  6. 

SERPENTINE.  (Magnesian  Silicate).  Composition,  Mg 
43%,  Si  43%.  Luster,  greasy  to  resinous; 
Color,  light  to  dark-green,  etc.;  Streak,  white  to  gray; 
Hardness,  2.5  to  4;  Gravity,  2.5 ;  Fracture,  uneven,  splintery; 
Tenacity,  lamellar,  foliated;  Crystals,  massive;  Fusi- 
bility, 5.5. 

Remarks:  The  Asbestos  minerals  are  found  in  Serpen- 
tine rocks  and  result  from  dissolved  material  separated  out 
and  crystallized  in  cavities  and  fissures.  The  following  are 
the  principal  Magnesium  minerals,  viz: — 

AMPHIBOLE.  Composition,  Mg,  Ca,  Si,  Etc.  Luster, 
vitreous;  Color,  white,  green  to  black; 
Streak,  white  or  gray;  Hardness,  5  to  6;  Gravity,  3;  Frac- 
ture, uneven;  Cleavage,  prismatic;  Tenacity,  brittle;  Crys- 
tals, monoclinic;  Fusibility,  3  to  4. 

Remarks:  The  minerals  Tremolite  and  Actinolite,  be- 
long to  the  Amphibole  group,  which  constitute  a  variety  of 
Asbestos  of  an  inferior  grade,  on  account  of  the  Calcium 
and  other  impurities,  suitable  only  for  manufacture  of 
boards,  roofings,  pipe  coverings  and  insulators.  The  market 
value  of  these  minerals  is  about  $12.00  a  ton. 

CHRYSOTILE.      Composition,    Mg,    Si,    O.      Luster,    silky; 
Color,  olive-green,  white  to  gray;  Fracture, 
fibrous;   Cleavage,   prismatic;   Tenacity,   sectile,   long   silky 
fibers,  tough ;  Infusible. 

Remarks:  Chrysotile  is  the  true  mineralogical  Asbestos, 
contains  no  lime,  and  this  will  usually  distinguish  it  from 


MINERALOGY  155 


other  varieties,  which  effervesce  slightly  in  acids.  This  min- 
eral crystallizes  in  fibers,  which  are  capable  of  being  woven 
into  cloth,  which  is  acid  and  fire-proof.  The  pure  mineral 
is  worth  about  $100.00  a  ton  and  the  pure  fiber  with  the 
silica  removed  is  worth  $400.00  per  ton.  Supply  of  this 
mineral  is  obtained  chiefly  from  Canada. 

TALC.  (Soapstone  or  Steatite).  Composition,  Mg  33%, 
Si  62%.  Luster,  pearly,  feel  greasy;  Colors, 
white,  green  in  various  shades ;  Streak,  white  to  gray ;  Hard- 
ness, 1  to  1.5;  Gravity,  2.5;  Fracture,  earthy;  Cleavage, 
basal;  Tenacity,  foliated,  compact;  Crystals,  orthorhombic ; 
Fusibility,  6. 

Remarks:  Talc  has  a  commercial  value  when  pure  and 
in  quantity  with  cheap  transportation  to  market.  American 
Talc  sells  from  $12.00  to  $20.00  a  ton;  French  Talc,  $35.00 
a  ton;  Italian  Talc,  $4'5.00  a  ton.  Talc  is  used  for  fire- 
proof paints,  coverings,  foundry  facings,  electric  insulators; 
also  used  in  manufacture  of  dynamite;  in  glazing  for  wall- 
papers in  toilet  powders,  and  in  dressing  leather. 

Carbon  (C)  Minerals 

71.  CARBON  (C)  occurs  in  its  native  purity,  crystallized 
in  the  Diamond,  and  in  a  modified  form  in  the  mineral 
Graphite.  The  group  of  minerals  known  as  Carbonates 
have  already  been  described  (Par.  18).  Carbon  is  a  con- 
stituent in  all  organic  matter,  both  animal  and  vegetable. 
Few  elements  are  capable  of  assuming  so  many  combinations 
as  Carbon  and,  for  this  reason,  it  has  been  called  the  "Enigma 
of  Science."  Wood,  charcoal  and  coke  are  familiar  examples 
of  Amorphous  (without  form)  carbon,  while  Coal  and 
Petroleum  are  simply  impure  forms  of  Carbon. 
DIAMOND.  Composition,  C  100%.  Luster,  adamantine; 


156    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Color,  white,  yellowish,  red,  blue,  green  and 
brown;  Hardness,  10;  Gravity,  3.5;  Tenacity,  brittle;  Crys- 
tals, isometric;  Infusible. 

Remarks:  Diamond  is  classed  as  infusible,  that  is,  it 
can  not  be  fused  or  melted,  but  it  will  burn  at  extremely 
high  temperatures  like  any  other  carbon  minerals. 

GRAPHITE.  (Plumbago  or  Black  Lead).  Composition, 
C  95  to  99% ;  Color,  iron-black  to  dark  steel- 
gray;  Fracture,  compact;  Cleavage,  basal;  Tenacity,  foliated, 
massive,  laminae  are  flexible;  Crystals,  hexagonal;  Fusibil- 
ity, 6. 

Remarks:  Graphite  is  used  in  the  manufacture  of  lead 
pencils.  It  is  a  commercial  mineral  and  has  a  market  value 
of  from  $50.00  to  $100.00  per  ton,  according  to  quality. 

The  amorphorus  variety  of  Graphite  is  of  little  value. 
The  foliated  variety  is  valuable  and  much  sought  after. 

(A)   HYDROCARBON  MINERALS 

The  Hydrocarbons  are  compounds  of  Carbon,  Oxygen 
and  Hydrogen,  and  include  mineral  oils  as  well  as  carbons. 
The  following  are  the  principal  Hydrocarbons: — 

ELATERITE    (Elastic  Bitumen).     Composition,   C  85%,   H 
15%.     Color,  brownish  -  black    to    jet-black; 
Hardness,  2;  Gravity,  1.25. 

Remarks:  Elaterite  is  very  elastic,  having  the  appear- 
ance of  india  rubber ;  it  is  malleable  and  burns  readily  with  a 
yellow  flame.  Ozocerite  is  similar  in  physical  characteristics 
and  composition.  These  minerals  are  thought  to  be  Petro- 
leum robbed  of  its  volatile  matter  and  are  chiefly  paraffine 
with  some  Naptha  and  Benzine.  Ozocerite  is  used  in  mak- 
ing wax  candles,  etc. 


MINERALOGY  157 


ASPHALTUM  (Wurtzelite).    Composition,  C,  H,  O;  Color, 
black;    Hardness,    1.25;   Gravity,    1.5.      Liquid 
when  hot,  sectile  when  cool,  tar-like  and  amorphous. 
PETROLEUM   (Rock  Oil).     Composition,  C,   H,  O.     This 
differs  with  localities  and  in  different  strata  in 
the  same  section.    Petroleum  is  found  in  the  rocks  of  all  ages 
from  the  Silurian  to  Tertiary,  usually  the  deeper  the  strata 
the  better  the  oil.     The  Tertiary  oils  have  a  heavy  asphalt 
base,  rendering  them  unsuitable  for  refining. 

(B)   MINERAL  COAL 

There  is  every  grade  of  coal  from  Peat  to  Graphite,  the 
deeper  the  coal  is  imbedded  the  purer  the  carbon,  while  sur- 
face or  Tertiary  coal  contains  impurities  and  volatile  matter. 
The  reason  for  this  is  that  the  coal  in  the  older  formations 
has  been  subjected  to  such  pressure  from  overlying  strata 
that  the  impurities  have  been  squeezed  out;  the  heat  of  the 
earth  too  tends  to  drive  off  volatile  matter.  This  is  proven 
by  the  alteration  of  Bituminous  coals  in  New  Mexico  to 
Anthracite  by  the  intrusion  of  porphyry  dikes.  The  follow- 
ing are  the  principal  Mineral  Coals: — 

LIGNITE    (Lignum-Wood).     Composition,   C   35   to   45% 
Volatile  matter,  (O,  H  &  N  S)  45  to  60% ;  Ash 
and  other  impurities,  7  to  15%. 

Remarks:  Lignite  Coal  is  so  named  because  formed 
from  buried  wood  so  shallow  and  so  little  compressed  and 
baked  that  the  grain  and  other  characteristics  of  original 
wood  may  be  noted  in  the  coal.  Lignite  coals  ignite  easily 
and  are  quickly  consumed. 

BITUMINOUS    (Soft  Coal).     Composition,   C  55   to  65%, 
H  10  to  20%,  O  15  to  25%,  N  3  to  5%,  S  1 
to  2%,  Ash  3  to  S%. 


158     PRACTICAL  GEOLOGY  AND  MINERALOGY 

Remarks:  Bituminous  Coal  carries  a  greater  percentage 
of  fixed  carbon  and  less  volatile  matter  than  Lignite. 
ANTHRACITE  (Hard  Coal).  Composition,  C  75  to  85%, 
H  2  to  5%,  O  6  to  10%,  Ash  7  to  10%. 
Hardness,  2  to  2.5;  Gravity,  1.61;  Fracture,  conchoidal; 
Burns  with  a  feeble  blue  flame.  Volatile  matter  ranges 
from  5  to  8%.  Difficult  to  ignite,  but  once  started  a  fire 
lasts  and  emits  little  smoke.  An  intermediate  coal  between 
Anthracite  and  Bituminous  Coal  is  sometimes  called  Semi- 
Anthracite. 

Silica  (Si)  Minerals 

72.  The  element  Silicon  (Si)  is  never  free.  It  is  next 
in  abundance  in  the  Earth's  crust  to  Oxygen,  with  which 
element  it  combines  to  form  Quartz,  Flint,  etc.,  called  Ox- 
ides of  Silicon.  Flint  is  uncrystallized  silica,  while  Quartz- 
is  nearly  always  crystalline  in  structure. 

There  are  a  number  of  varieties  of  Quartz  which  have 
the  same  physical  and  chemical  properties,  only  differing  in 
color,  which  is  due  to  the  presence  of  other  elements  as 
impurities. 

QUARTZ.     Composition,  Si  46.67%,  O  53.33%;  Hardness, 
7;  Gravity,  2.5  to  2.8;  Color,  white  to  yellowish. 
Luster,  vitreous,  transparent  to  opaque.    The  following  Gem 
Stones  are  varieties  of  quartz,  viz: — 

(1)  Rock  Crystal — white. 

(2)  Rose  Quartz — pink. 

( 3 )  Amethyst — purplish. 

(4)  False  Topaz — yellowish. 

( 5 )  Chrysoprase — apple-green. 

(6)  Carnelian — bright-red. 

(7)  Agate — cloudy. 

(8)  Onyx — various  colors. 


MINERALOGY  159 


(9)    Bloodstone — green  with  blood-colored  spots. 

SILICATE  MINERALS 

Silicates  are  compounds  of  Silicon,  Oxygen  and  another 
element.  The  silicates  of  the  metals  have  already  been 
described.  The  following  are  the  principal  Gem  Stone 
Silicates,  viz: — 

GARNET.    Composition,  Si  36%,  Al  20%,  Fe  and  O  43%. 
Luster,  vitreous ;  Color,  various  from  red  to  black. 

TOURMALINE.    Composition,  Si  39%,  Al  30%,  Mg  8%,  B, 
Fe,   O,   etc.      Hardness,    7.5;   Gravity,    3; 
Color,  blue-brown  to  red. 

TOPAZ.     Composition,  Si  16%,  Al  55%,  Fl,  etc.     Colors, 
various,  yellow,  white,  bluish,  red,  etc. 

COMMON  SILICATE  ROCKS 

PYROXINE.     Composition,  Si  55%,  Ca  23%,  Mg  16%,  Fe, 
Mn,  O.     Hardness,  5  to  6;  Gravity,  3.5;  Color, 
greenish,  white  to  dark. 

ANDESITE.     Composition,   Si  59%,  Al  25%,  Ca  7%,  Na 
7%.     Color,  whitish,  grayish  to  bluish;  Hard- 
ness, 6;  Gravity,  2.7. 

HORNBLENDE.     Composition,  Si  48%,  Ca  10%,  Mg  13%, 
Mn,  Fe  and  O.     Color,  black  to  greenish; 
Hardness,  5  to  6.1 ;  Gravity,  3.2. 

What  Are  the  Gangue  Minerals? 

73.  Metal  Minerals  are  found  in  veins  or  lodes  mixed 
with  other  minerals  called  Gangue  or  vein  mineral.  In 
metalliferous  veins,  the  Gangue  matter  is  usually  more  or 
less  banded  or  arranged  in  streaks  or  layers  and  a  deter- 
mination of  the  different  gangue  minerals  and  relative  pro- 
portions, is  often  very  desirable. 


160     PRACTICAL  GEOLOGY  AND  MINERALOGY 

The  following  are  the  minerals  usually  associated  with 
metal  mineral  veins: — 

(1)  Quartz. 

(2)  Calcite. 

(3)  Dolomite. 

(4)  Barite  or  Heavy  Spar. 

(5)  Fluorite  or  Fluor-Spar. 

(6)  Iron,  oxide  or  pyrite. 

(7)  Talc. 

Other  minerals  sometimes  found  either  in  or  associated 
with  veins  are: — 

(a)  Porphyry. 

(b)  Granite. 

(c)  Andesite. 

(d)  Rhyolite,  and  other  igneous  rocks. 

These  minerals  have  already  been  described,  and  this 
knowledge  will  enable  the  reader  to  name  the  gangue  min- 
erals in  most  any  ore  and  form  an  estimate  of  the  propor- 
tions of  each  constituent. 

How  to  Make  Practical  Application  of  Physical 
Properties 

74.  We  have  briefly  noted  Physical  Propetries  common 
to  minerals  and  have  grouped  and  classified  the  most  impor- 
portant  according  to  their  physical  properties  and  Chemical 
proportions.  Such  lessons  are  mainly  theoretical  and  in 
order  to  make  this  knowledge  of  much  value  it  must  be  put 
into  practice.  Any  one  with  mineral  specimens  of  deter- 
mined purity  can  test  them  by  all  the  physical  properties 
named  in  the  table  for  that  particular  mineral,  and  verify 
their  characteristics  as  well  as  the  identity  of  the  mineral 
itself.  This  is  the  usual  course  in  the  study  of  mineralogy. 


MINERALOGY  161 


Having  the  answer  to  the  problem  in  the  mineral  itself  duly 
determined,  it  is  relatively  easy  to  work  backwards  to 
prove  the  elements  that  enter  into  its  composition.  In  field 
practice,  however,  the  conditions  are  exactly  reversed.  The 
mineral  specimen  found  is  the  problem  and  the  answer  must 
be  worked  out  by  a  regular  process  and  the  answer  must  come 
as  a  result  of  careful  examination  and  patient  work.  The 
following  is  suggested  as  a  working  plan  in*  the  determination 
of  a  mineral: 

An  unknown  mineral  is  submitted  for  test.  We  examine 
it  and  note  its  Luster  is  metallic.  Note  on  a  piece  of  paper, 
"Luster  Metallic."  Next  we  note  its  color,  as  "lead  gray," 
and  Streak  the  same.  Its  general  appearance  indicates  it  is  a 
Sulphide  of  some  kind.  Note  "Sulphide"  on  record  paper. 
Now  examine  its  hardness.  It  is  soft,  the  finger  nail  scratch- 
es it  slightly  and  a  copper  coin  will  scratch  it.  Note  its 
hardness  as  "under  3,"  perhaps  2.5.  Next  note  its  weight 
in  the  hand,  comparing  it  with  a  piece  of  quartz  or  granite  of 
similar  size  whose  known  Gravity  is  about  2.5.  The  speci- 
men appears  about  three  times  heavier.  Note  "Gravity,  say, 
7."  Take  the  point  of  a  pocket  knife  and  see  if  you  can  cut 
it.  Does  it  powder,  or  cut  off  in  flakes?  If  the  latter,  note 
"Sectile."  Break  it  with  a  hammer,  if  you  have  one,  if  not 
take  another  rock  and  strike  it.  Does  it  fracture  easily? 
What  kind  of  a  surface  does  it  leave,  smooth  or  uneven? 
If  "uneven"  examine  and  note  if  surface  has  shell-like 
cavities  and  projections.  If  so  note  "Conchoidal  Fracture." 
Next  note  the  crystals  with  the  naked  eye  and  with  a  lens. 
Can  you  detect  angles  and  faces  of  cubes?  If  so  mark  it 
"Crystals  Isometric."  Before  leaving  it  take  a  small  splinter 
of  the  mineral  and  subject  it  to  the  candle  flame.  If  it  melts 
note  "Fusibility  2  or  under."  If  you  have  familiarized  your- 


162    PRACTICAL  GEOLOGY  AND  MINERALOGY 

self  with  the  physical  properties  of  common  minerals,  you 
can  readily  name  the  mineral.  From  our  examination  three 
things  stand  out  prominently :  ( 1 )  It  is  very  heavy ;  its 
weight  must  be  due  to  its  metal  content.  We  infer  it  is 
either  a  Gold,  Silver  or  Lead  mineral.  Let  us  see  what  Gold 
mineral  it  might  be.  A  Gold  Telluride  is  the  only  one  that 
has  any  of  the  characteristics  named.  No  Telluride  mineral 
has  Isometric  Crystals,  so  we  eliminate  that  from  considera- 
tion. We  must  now  determine  whether  Silver  or  Lead  min- 
eral. Lead  minerals  are  nearly  all  brittle  and  powder  under 
the  knife  point.  This  does  not,  but  cuts  off  in  flakes,  so  we 
eliminate  Lead  from  the  problem  and  decide  it  is  a  Silver 
mineral.  We  have  already  decided  it  is  a  sulphide  from  its 
appearance  and  the  sulphur  fumes  in  the  candle  flame.  There 
are  several  Silver  minerals  that  have  sulphur  in  their  com- 
position. Is  it  Argentite  ?  Now  look  at  the  physical  proper- 
ties named  for  that  mineral ;  you  find  on  comparing  with  your 
notes  that  they  correspond.  It  is  Argentite;  the  problem  is 
solved.  Note  the  Composition,  Ag  87%,  S  12%.  Chemical 
analysis  is  unnecessary.  Many  other  minerals  are 
as  easily  determined  by  this  same  method.  We  took  a  com- 
mon mineral  and  the  problem  was  not  so  difficult,  but  in 
actual  practice  it  is  not  so  easy,  especially  in  the  field.  Pure 
minerals  are  rare,  but  even  in  a  mixed  mineral  some  crystal- 
line particle  may  often  be  observed  which  serves  to  distin- 
guish it  by  physical  properties. 

In  concluding  the  subject  of  Mineralogy,  the  author  can 
not  forbear  again  urging  the  necessity  of  securing  true 
mineralogical  specimens  from  some  reputable  dealer  in 
minerals,  especially  such  as  you  are  most  interested  in,  as 
comparisons  can  be  quickly  made  and  you  will  soon  become 


MINERALOGY  163 


so  familiar  with  the  common  minerals  as  to  be  able  to  classify 
them  off-hand. 

How  to  Estimate  the  Value  of  Ores 

An  ore  is  usually  a  mixed  mineral,  often  made  up  of 
several  minerals  together  with  gangue  minerals,  the  whole 
constituting  a  vein  filling. 

Suppose  in  a  pound  average  sample  of  a  copper  ore  that 
one-tenth  of  the  mass  is  made  up  of  Azurite  and  Malachite, 
usually  surface  ores.  By  referring  to  the  tables  you  will  see 
Malachite  and  Azurite  when  pure  average  about  70% 
copper. 

One-tenth  of  a  ton  is  200  pounds;  at  70%  copper  would 
be  140  pounds  copper  metal  to  the  ton.  Multiplying  by  15 
cents,  value  of  one  pound  of  copper,  would  give  an  estimate 
value  of  $21  per  ton  of  ore. 


PART  IV 

MINERAL 
DEPOSITS 


Part  IV 

MINERAL  DEPOSITS 

1.  Under  the  subject  Mineralogy,  we  learned  that  all 
except  those  found  native,  are  compounds  of  two  or  more 
primary  elements,  usually  crystallized  into  geometric  forms, 
with  a  definite  proportion  of  each  combined  element.    It  was 
also  shown  that  such  mineral  crystals  result  from  the  proces- 
ses known  as  Fusion,   Vaporization  and  Solution;  the  ele- 
ments  separating   out    and    combining   in    accordance   with 
natural  laws. 

It  must  not  be  assumed  that  all  minerals  occur  in  a  pure 
state;  except  in  a  few  instances,  mineral  deposits  of  commer- 
cial importance  are  found  associated  with  the  more  common 
earth  minerals  known  as  Gangue,  so  that  the  result  is  a 
mixed  mineral,  and  this  is  what  the  practical  miner,  as  a  rule, 
has  to  deal  with  in  the  field. 

What  Are  the  Relative  Proportions  of  the  Elements? 

2.  Of  the  eighty  elements   that  make  up   the  earth's 
crust,  six  compose  nearly  95%  and  seven  additional  swell 
the  amount  to  99%  of  the  crust.     Sections  of  the  crust  have 


168     PRACTICAL  GEOLOGY  AND  MINERALOGY 

been  analyzed  and  an  estimate  made  of  the  proportions  of  the 
most  abundant  elements,  as  follows: — 

Oxygen    45    % 

Silicon    25    % 

Aluminum    10    % 

Iron   B.5% 

Calcium     6    % 

Potassium,  Sodium,  Carbon  and  Magnesium 3.5% 

Sulphur,  Hydrogen,  Chlorine  and  Nitrogen 1.5% 

67  Other  Elements 0.5% 


Total   100.00% 

This  table  shows  that  sixty-seven  elements,  which  include 
all  the  "precious  metals,"  comprise  only  one-half  of  one  per 
cent  of  the  earth's  crust.  Some  authorities  estimate  the 
precious  metals  compose  less  than  one  part  of  one  thousand, 
or  less  than  one-tenth  of  one  per  cent  of  the  mass. 

These  are  only  approximate  proportions,  but  whether 
accurate  or  not,  it  is  quite  plain  that  minerals  of  commercial 
value  are  rare,  although  the  elements  are  everywhere  present 
in  finely  disseminated  particles.  These  can  only  become  of 
importance  when  concentrated  by  nature's  processes  into 
what  are  called  MINERAL  DEPOSITS.  For  example — Gold 
is  one  of  the  rare  eelments,  yet  it  is  found  in  the  rocks  of  all 
ages,  and  in  the  waters  of  rivers,  seas  and  oceans.  Analyses  of 
ocean  waters  show  40  to  50  miligrams  (about  1-20  grain)  to 
the  ton  of  water.  This  may  seem  trifling,  but  when  it  is 
considered  that  the  seas  cover  three-fourths  of  the  earth's 
surface,  and  contain  multiplied  millions  of  tons,  the  total 
amount  of  gold  held  in  suspension  or  in  solution  is  enormous, 
and  if  it  could  all  be  extracted  economically,  gold  would  be 
too  abundant  for  coinage  into  money. 


MINERAL  DEPOSITS  169 

Since  the  precious  mineral  elements  are  everywhere  pres- 
ent in  such  small  proportions,  and  only  occasionally  found  in 
commercial  quantities,  it  is  important  to  know  nature's  pro- 
cesses of  segregating  and  collecting  the  rare  elements  into 
what  are  known  as  Mineral  Deposits. 

What  Is  the  Origin  of  Mineral  Deposits? 

3.  The  genesis  (beginning)  of  mineral  deposits  is  a 
subject  not  fully  understood,  hence  cannot  be  regarded  as  an 
exact  science,  and  it  becomes  necessary  to  theorize  in  our 
endeavor  to  ascertain  the  truth. 

To  the  practical  man,  theories  may  often  appear  useless, 
but  in  the  absence  of  positive  knowledge  this  is  our  only 
recourse.  We  are  not  without  facts  as  to  the  occurrence  of 
mineral  bodies,  but  the  variety  in  form  and  structure  of  such 
deposits  throughout  the  world  has  resulted  in  several  theories 
as  to  their  origin,  each  of  which  is  based  on  evidence  more  or 
less  convincing  in  particular  cases. 

A  knowledge  of  these  origin  theories  is  important  inas- 
much as  they  represent  the  most  advanced  thought  on  this 
subject.  And  from  the  further  fact  that  the  successful 
development  and  valuation  of  a  mine  requires  a  definite 
idea  of  the  geologic  forces,  the  chemical  and  mechanical 
processes  which  combined  to  produce  the  mineral  deposit. 
A  knowledge  of  these  fundamental  principles  enables  a 
practical  mining  man  to  formulate  a  definite  scientific  plan 
of  operation  without  which  everything  must  be  left  to 
"chance"  and  almost  certain  failure. 

There  are  two  general  theories  as  to  the  original  source 
of  the  metallic  elements,  viz:  — 

(a)  Surface  Origin, — from  sea  water,  and 

(b)  Subterranean  Origin, — from  molten  interior  of  the 
earth. 


170    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Both  of  these  grow  out  of  the  theories  as  to  the  origin  of 
the  earth  itself.  (See  Nebular  and  Meteoritic  Theories.) 

What  Is  the  Sea  Water  Theory? 

4.  This  theory,  in  general,  supposes  that  all  the  metall- 
lic  minerals  in  or  upon  the  earth  are  derived  from  the  waters 
of  the  seas.  If  we  accept  the  Nebular  Hypothesis  of  the 
origin  of  the  Solar  System,  we  may  believe — 

(a)  That    in    the    "beginning,"    all    matter    was    in    a 
gaseous  state,  and 

(b)  That  as  the  earth  cooled  so  far  as  to  form  water  on 
its  surface,  this  hot  primeval  ocean  held  in  solution    (dis- 
solved)  all  the  metallic  elements,  condensed  from  original 
gaseous  matter; 

(c)  That  the  metallic  elements  were  separated  out  by 
living  organisms,  or  through  their  dead  bodies,  the  accumu- 
lations of  which  brought  the  metallic  elements  within  the 
sedimentary    rock   strata,    where    the   circulation   of    under- 
ground waters,  through  previously  formed  fissures  and  cav- 
ities, formed  the  mineral  deposits  we  find  within  the  earth 
today. 

(d)  That  when  metals  are  present  in  igneous  rocks,  they 
were  fused  from  sediments,  and  that  in  the  process  of  the 
ages   all   rocks   have   been   partly   or   completely   fused    and 
worked  over  many  times,  so  that  in  brief  all  mineral  deposits 
^ear  enough  to  the  surface  to  be  reached  by  man  contain 
only  such  metallic  elements  as  were  originally  dissolved  in 
the  sea  water. 

Let  us  examine  the  evidence  to  sustain  this  belief: — 
(1)   This  theory  is  based  upon  the  demonstrated   fact 
that  sea  water  does  contain  all  the  metallic  elements.   (See 


MINERAL  DEPOSITS  171 

Par.  2.)  But  this  fact  does  not  prove  that  these  elements 
were  not  first  washed  from  the  igneous  land  rocks.  In  fact 
presence  of  gold,  for  instance,  in  ocean  waters  adjacent 
to  metalliferous  regions  like  Australia  and  the  Pacific  Coast 
of  North  America,  in  greater  percentage  than  elsewhere, 
seems  to  be  against  this  theory. 

(2)  Science   is    agreed    is   agreed    that    lime   rocks    are 
formed  from  the  shells  and  bones  of  sea  animals,  and  since 
the  base  of  limestone  is  the  metallic  element  Calcium,  it  is 
argued  that  all  other  metallic  elements  might  well  be  derived 
in  a  similar  manner.     But  this  claim  does  not  take  into  con- 
sideration that  the  mineral  existed  before  the  animal,  and  the 
same  objection  holds  against  the  original  source  of  quartz, 
as  the  result  of  secretions  of  sea  animals. 

(3)  The  presence  of  metallic  elements  in  sedimentary 
rocks,  it  is  claimed,  tends  to  prove  sea  water  origin.     This 
claim  is  not  given  much  credit,  as  it  is  equally  evident  that 
the  insignificant  percentage  of  metallic  elements  in  stratified 
rocks  might  easily  be  derived  from  erosion  and  corrosion  of 
igneous  rocks. 

(4)  Some  deep  mines  that  occur  near  oceans  have  been 
found  to  contain  salt  water,  notably  in  Australia,  and  the 
presence  of  chloride  minerals  in  many  places  tends  to  prove 
at   least   some   connection   between   sea  water   and   mineral 
deposits  found  in  the  earth's  crust. 

What  Is  the  Igneous  or  Subterranean  Theory? 

5.  Founded  also  on  the  theories  of  the  origin  of  Solar 
System  is  the  claim  that  all  metallic  minerals  have  their 
source  within  the  earth.  Those  who  support  the  subterran- 
ean theory  claim: — 

(a)   That  as  the  earth  cooled,  those  elements  like  iron, 


172     PRACTICAL  GEOLOGY  AND  MINERALOGY 

cobalt,  nickel,  platinum,  etc.,  that  fuse  only  at  very  high 
temperatures,  condensed  from  a  gaseous  form  to  liquid. 
On  further  cooling  they  became  plastic  and  formed  a  nucleus 
of  the  globe,  around  which  in  succession  the  other  elements, 
lower  in  the  scale  of  fusibility,  gradually  arranged  them- 
selves in  the  process  of  condensing,  until  all  the  solid  ele- 
ments were  included  in  the  sphere.  Lastly  water  was 
formed  by  the  union  of  oxygen  and  hydrogen,  leaving 
behind  the  atmosphere,  a  mixture  of  gases  somewhat  as  we 
find  it  today. 

Let  us  see  what  evidence  there  is  to  sustain  this  subter- 
ranean theory. 

( 1 )  The  weight,  or  specific  gravity  of  the  earth  as  a 
whole,  as  computed  by  scientists,  is  about  three  times  that  of 
the  outer  crust  known  to  man. 

(2)  The  heavier  and  difficultly  fusible  metals  are  pres- 
ent in  greater  abundance  in  the  primitive,  crystalline  rocks. 

(3)  The   undisputed   and   otherwise   unexplainable   fact 
that  the  earth  is  a  great  magnet,  which  might  well  result 
from  a  core  within  the  earth  of  the  magnetic  minerals, — 
iron,  etc. 

(4)  The  vapors  of  volcanoes  are  laden  with  metallic 
elements  and  the  waters  from  hot  springs  are  charged  with 
dissolved  mineral  matter. 

Unlike  the  claims  for  the  sea  water  theory,  the  evidences 
above  named  are  not  open  to  such  serious  objections,  so  that 
it  appears  plain  that  the  immediate  source  of  metallic  metals 
usually  found  in  veins  is  within  the  earth,  although  they  may 
have  been  derived  partially,  or  wholly,  from  underground 
passages  leading  to  the  seas  as  the  primary  source. 


MINERAL  DEPOSITS  173 

Conclusions  from  the  Evidence 

6.  Each    of    the    theories    has    the   support    of    learned 
authorities,  but  the  igneous  theory  appears  to  be  worthy  of 
the  most  consideration  on  account  of  the  preponderance  of 
the  evidence  in  its  favor;  but  whether  the  original  source  of 
metals  is  within  the  earth  or  not,  it  would  be  contrary  to 
the  known  economy  of  nature  to  thus  lock  up  the  metallic 
contents  permanently.     So,  assuming  that  the  metallic  bur- 
den of  sea  water  was  derived  from  the  igneous  rocks,  nature's 
processes  must,  in  some  way,  return  the  metallic  elements  to 
the  solid  crust,  as  surely  as  the  ocean  water  returns  to  the 
land  in  the  form  of  rain. 

How  Are  Mineral  Deposits  Formed? 

7.  Since  metallic  elements  are  everywhere  present,  but 
in   such   minute   quantities   as  to   be  valueless,   it   must   be 
apparent   that   these   must   be   collected    and   segregated    by 
nature's  forces  in  order  to  be  of  use  to  man.     In  the  animal 
and  vegetable  kingdoms,   organic  matter  separates  out  into 
groups  or  families,  in  accordance  with  natural  laws,  and  in 
the   mineral   kingdom   there   is   a  similar   tendency.     Thus 
water  is  ever  moving,  collecting  and  aggregating  on  its  way 
to  the  great  *  'mother  of  waters" — the  ocean.     We  explain 
this  in  obedience  to  the  great  law  that, — "Water  seeks  its 
level,"  and  it  is  natural  to  assume  that  there  is  a  similar 
movement  of  metallic  elements  to  separate  out  and  aggregate 
each  after  its  kind.    We  can  only  explain  this  by  saying  that 
"like   attracts   like,"   and    the   result   is   a   concentration  of 
metallic  elements  into  what  we  call  mineral  deposits. 

What  Are  the  Concentrating  Agencies? 

8.  There  are  a  number  of  forces  which  have  been  acting 
throughout  the  ages  collecting  the  widely  distributed  metallic 


174     PRACTICAL  GEOLOGY  AND  MINERALOGY 

elements  into  mineral  deposits  for  the  use  of  man.  These 
forces  act  singly  and  in  combination,  but  they  may  never- 
theless all  be  classified  under  two  heads,  as  follows: 

(1)  Mechanical  Agencies. 

(2)  Chemical  Agencies. 

(1)  Mechanical  Agencies  include   forces  that  operate 
in  obedience  to  natural  laws,  such  as  gravity,  mineral  attrac- 
tion, etc.     They  produce  no  real  change  in  the  elements 
themselves.     The  formation  of  placer  beds  by  glacial  action, 
and  by  the  movement  of  water  from  the  heights  to  basins 
or  river  channels  below,   illustrate  this  mechanical  action. 
The  specific  gravity   (See  Page  111)  of  the  metals  usually 
found  in  placers,  being  greater  than  the  associated  elements, 
the  lighter  are  carried  along  with  the  current,  while  the 
heavier  lag  behind   and   tend   to  settle  and   accumulate  in 
favored  spots  to  form  placer  beds.     There  is  also  a  kind  of 
chemical  action  which  assists  the  mechanical,  but  this  will 
be  explained  later. 

(2)  The   Chemical  Agencies   are   more   complex,   and 
hence  not  so  easily  explained  or  understood.     This  subject 
propery  belongs  to  Physics  and  Chemistry,  but  inasmuch  as 
ore   deposits   are   due   largely  to   chemical   agencies,   a   few 
elementary  principles  are  necessary  to  understand  the  forma- 
tion of  ore  deposits.     These  agencies  while  called  Chemical, 
involve  physical  forces  to  some  extent,  but  may  be  classified 
as  follows: 

(a)  Vaporization, 

(b)  Fusion, 

(c)  Sublimation. 

(d)  Solution. 

9.      (a)    Vaporization  is  the  process  of  changing  a  liquid 
to  a  gas,  or  vapor.     A  simple  process,  familiar  to  all,  is  the 


MINERAL  DEPOSITS [75 

change  of  water  to  vapor,  as  in  steam  due  to  the  agency  of 
heat.  When  water  is  exposed  to  the  influence  of  the  at- 
mosphere and  the  sun's  heat,  it  passes  slowly  into  the  gaseous 
state,  leaving  behind  its  mineral  burden,  and  the  process  is 
called  Evaporation.  Beds  of  salt,  soda  and  some  gypsums 
are  formed  by  this  simple  natural  process. 

When  a  liquid  or  molten  metal  is  subjected  to  the  proper 
degree  of  heat,  it  also  passes  into  a  gaseous  state,  and  it  is 
then  said  to  Volatilize.  All  known  elements  are  volatile  at 
temperatures  considerably  above  their  respective  fusing 
points. 

10.  (b)   Fusion  is  a  process  that  results  when  mineral 
elements  are  subjected  to  the  degree  of  heat  necessary  to  melt 
them,  as  in  smelting.    When  fusion  takes  place,  the  metallic 
elements  separate  out  from  the  mass,  each  after  its  kind,  or 
as  an  alloy,  and  if  conditions  are  favorable  upon  cooling  min- 
eral crystals  will  form.     It  is  believed  that  the  heat  of  the 
earth,  in  the  Molten  or  Flowage  Zone,  is  sufficient  to  fuse 
all  matter,  and  as  a  result  the  metallic  elements  are  segre- 
gated and  concentrated  out  of  the  molten  mass.     The  erupt- 
ive forces  expel  this  mineral  matter  through  fissures  in  the 
crust,  as  in  the  case  of  the  minerals  magnetite  and  pyrrho- 
tite,  to  fill  such  cavities  with  ores.     It  is  not  certain  that  any 
of  the  precious  mineral  deposits  are  formed  by  the  direct 
process  of  fusion,  but  many  so-called  "blow-outs"  of  metallic 
minerals  and  some  placer  nuggets  may  perhaps  be  traced  to 
such  an  origin.     Few  veins  are  thus  mineralized,  however. 

11.  (c)   Sublimation  is  the  process  by  which  metallic 
vapors  are  condensed  and  solidified,  by  coming  in  contact 
with  a  cool  surface,  when  a  coating  or  deposit  is  formed, 
called  a  sublimate.  It  is  a  purifying  and  concentrating  process 
combined,  and  is  analagous  to  distillation  in  liquids. 


176    PRACTICAL  GEOLOGY  AND  MINERALOGY 

A  familiar  example  illustrating  the  processes  of  fusion, 
volatilization  and  sublimation  is  shown  in  Fig.  46.  A  bit 
of  sulphur  is  placed  on  a  knife  blade  held  over  a  candle 
flame  in  such  a  way  as  to  avoid  setting  fire  to  the  sulphur, 
the  sulphur  first  melts  and  forms  a  liquid  (fusion),  which 
grows  smaller  and  smaller  from  arising  vapors  (Volatiliza- 
tion) ;  if  a  cold  plate  is  held  above  the  escaping  sulphur  gas, 
it  is  deposited  there  as  "flowers  of  sulphur"  (Sublimation), 
and  the  element  thus  condensed  is  called  a  sublimate.  This 
is  purely  a  physical  change,  but  if  the  sulphur  is  ignited 
(burned)  an  entirely  different  process  ensues.  Now  sulphur 


Fig.  46 


The  sulphur  that  we  cause  to  evaporate  remains  sulphur 
(physical  phenomenon). 

is  classed  as  a  Non-Metal,  but  it  serves  to  illustrate  the 
processes  named  as  well  as  a  metal ;  when  it  is  remembered 
that  all  metals  are  volatile  at  appropriate  temperatures,  and 
that  the  heat  of  the  earth's  interior  is  sufficient  to  change 
every  element  into  the  gaseous  state,  we  may  understand  how 
metallic  vapors  escaping  through  open  fissures  in  the  earth's 
crust  and  coming  in  contact  with  cool  surfaces  may  form  a 
deposit  or  sublimate  of  the  metals  to  constitute  an  ore  body. 
Examples  are  not  wanting  in  nature  of  minerals  deposited  by 
sublimation.  Metallic  crusts  are  thus  formed  in  cracks  or 
fissures  adjacent  to  expiring  volcanoes;  sixteen  different 


MINERAL  DEPOSITS 177 

metals  have  been  extracted  from  the  vapors  arising  from  the 
volcano  Vesuvius.  No  ore  deposits  can  be  formed  in  an 
active  volcano,  because  of  the  absence  of  a  cool  surface  to 
condense  the  metallic  vapors.  Many  so-called  "ore  chim- 
neys" in  veins  are  believed  to  have  been  formed  by  sublima- 
tion. 

12.  (d)  Solutions.  All  metals  are  more  or  less  soluble 
in  acids  and  alkalies,  especially  when  the  metallic  particles 
are  in  a  finely  divided  state.  The  earth's  crust  contains  many 
acid  and  alkali  minerals,  and  these  are  dissolved  or  rendered 
soluble  by  water  circulating  through  fissures  and  cavities  in 
the  Oxide  Zone,  which  solutions  in  turn,  assisted  by  the 
atmospheric  gases,  attack  the  metallic  elements  to  render 
them  soluble.  Heat  too  assists  in  dissolving  mineral  ele- 
ments, and  thus  the  process  of  Solution  continues  and  tends 
to  concentrate  the  dissolved  mineral  matter  into  cavities  or 
fissures.  It  requires,  however,  another  process  to  separate 
out  the  metallic  elements  from  the  solution  to  form  ore 
deposits  which  is  known  as  precipitation. 

Precipitation.  This  process  is  a  literal  "throwing- 
down"  of  the  metallic  burden  of  a  solution  into  a  solid  form. 
A  precipitant  may  be  an  element  or  a  compound,  different 
from  that  contained  in  the  solution  itself,  as  a  solid,  liquid  or 
gas.  Electricity,  which  is  everywhere  present,  acts  as  one  of 
the  most  powerful  precipitants. 

Precipitation  of  metals  from  solution  is  analagous  to 
sublimation  of  metallic  vapors.  A  simple  experiment  to 
illustrate  precipitation  is  to  dissolve  a  bit  of  silver  metal  in 
nitric  acid,  after  which  add  a  little  common  table  salt 


178    PRACTICAL  GEOLOGY  AND  MINERALOGY 

(Chloride  of  Sodium),  when  a  white  substance  settles  out, 
or  is  "thrown  down"  as  a  precipitate,  known  as  a  silver 
chloride. 

Some  metals  precipitate  other  metals  from  their  solu- 
tions. Thus  silver  is  thrown  down  by  copper,  copper  by 
iron  and  lead  by  zinc.  Hot  metallic  solutions  may  often  be 
precipitated  by  cold  water,  and  cold  metal  solutions  may 
likewise  be  precipitated  by  hot  water.  The  water  of  many 
mines  carries  considerable  copper  in  solution.  In  the  early 
days  of  copper  mining,  bright  fellows  bought  waste  water 
from  such  mines  for  a  mere  pittance.  They  precipitated  the 
metallic  copper  by  running  the  water  over  tin  cans  and  scrap 
iron;  in  this  very  simple  and  effective  way  they  made  much 
money.  The  water  in  many  copper  mines  has  its  metallic 
content  precipitated  on  iron  pyrites  to  form  native  copper. 

Laboratory  experiments  have  proven  that  gold  is  also 
precipitated  from  solutions  on  iron  pyrites  after  a  long 
period.  Gold  is  also  precipitated  from  alkaline  solutions 
(Cyanide)  by  zinc  and  electricity. 

If  these  principles  are  borne  in  mind,  the  concentration 
of  metallic  elements  to  form  ore  deposits  will  be  more  readily 
understood. 

When  it  is  considered  that  all  the  reagents  known  to 
science,  and  perhaps  some  about  which  nothing  is  known, 
are  found  in  nature's  vast  laboratory,  and  that  these  pro- 
cesses have  been  at  work  throughout  the  ages  concentrating 
the  metallic  elements  from  the  great  earth  mass  to  form  ore 
deposits  for  the  use  of  man,  we  may  realize,  in  part  at  least, 
how  important  it  is  to  understand  nature's  laws  and  work  in 
harmony  therewith  in  all  mining  operations. 


MINERAL  DEPOSITS 179 

POPULAR  THEORIES  AS  TO  THE  GENESIS  OF 
ORE  DEPOSITS 


13.  Ever  since  lode  mining  came  into  existence,  man 
has  striven  to  find  out  nature's  secret  processes  of  mineraliz- 
ing veins.     The  great  varieties  of  ore  deposits  have  given 
rise  to  several  theories.    The  earlier  of  these  have  now  been 
practically  discarded,  but  there  are  many  who  still  cling  to 
these  primitive  ideas.     Thus  every  mining  man  should  be 
familiar  with  the  merits  and  inconsistencies  of  each  in  order 
to  keep  abreast  of  the  times,  as  well  as  to  avoid  the  most 
common  errors  in  mining. 

These   different    origin    theories    may   be   classified    as 
follows : 

( 1 )  Contemporaneous  Formation. 

(2)  Igneous  Injection. 

(3)  Electric   Currents. 

(4)  Descending  Waters. 

(5)  Sublimation. 

(6)  Lateral  Secretion. 

(7)  Ascending  Waters. 

(8)  Replacement. 

( 1 )   What  Is  the  Theory  of  Contemporaneous      . 
Formation  ? 

14.  This  is  a  theory  held   by  early  writers,   and   the 
supposition  was  that  the  veins  were  formed  and  mineralized 
at  the  same  time  the  enclosing  rocks  were  formed,  and  that 
rich  mineral  deposits  were  a  mere  incident  or  accident.    This 
theory  may  be  accepted  as  regards  the  formation  of  sedi- 
mentary mineral  deposits,  but  so  far  as  ore  deposits  in  veins 


180     PRACTICAL  GEOLOGY  AND  MINERALOGY 

are  concerned  it  is  contrary  to  all  known  science  and  may  be 
dismissed  from  further  consideration. 

(2)    What  Is  the  Theory  of  Igneous  Injection? 

15.  This  theory  assumes  that  all  veins  were  formed  and 
mineralized  by  injection  of  igneous  matter  from  below,  and 
that  this  molten  magma  contained  all  the  metallic  elements 
found  in  ore  deposits.    This  belief  proceeds  from  the  proven 
fact  that  all   igneous   rocks  contain    metallic    elements   in 
greater  or  less  degree.     When  we  consider,   however,   the 
banded  structure  of  many  veins,  and  the  irregular  occurrence 
of  ore  in  shoots  or  pockets  within  the  vein  material   this 
theory  is  unsatisfactory  and  is  now  generally  discarded  by 
scientists.    While  there  may  be  instances  of  igneous  injection 
of  metallic  minerals  into  veins,  they  are  rare  and  are  not  well 
sustained  by  evidence.    Therefore  this  theory  does  not  merit 
serious  consideration. 

(3)   What  Is  the  Electric  Current  Theory? 

16.  The   Electric  Theory   had   strong  support   a   half 
century   ago,    but   the  later   authorities   have   raised   serious 
objections  to  it.     There  is,  however,  a  solid  foundation  for 
this  theory  in  the  fact  that  the  earth  is  a  great  magnet,  and  as 
friction  is  known  to  develop  electricity,  it  appears  reasonable 
that  earth  movements  developed  powerful  electric  currents 
during  the  period  of  formation  and  filling  of  veins. 

Electric  currents  have  been  proven  to  exist  in  veins  today, 
and  this  is  recognized  as  a  most  effective  agent  in  metallurgy, 
as  a  precipitant,  which  makes  it  seem  probable  that  this  is 
one  of  the  great  natural  forces  within  the  earth  to  "throw 
down"  the  metallic  elements  from  mineral  solutions,  but 
there  is  little  or  no  evidence  to  sustain  the  belief  that  the 


MINERAL  DEPOSITS  181 

electrical  forces  carry  the  metallic  elements  into  or  through 
the  veins. 

(4)   What  Is  the  Theory  of  Descending  Waters? 

17.  This  theory  follows  in  part  the  supposition  that  all 
metals  are  derived  from  the  sea  water,  and  that  the  metallic 
burden  was  deposited  in  fissures  and  cavities  from  the  waters 
flowing  over  them.  There  are  instances  of  minerals  occur- 
ring in  the  sedimenaary  rock  fissures,  like  lead,  zinc,  etc., 
that  may  have  been  thus  formed,  but  deposits  in  igneous  or 
metamorphic  rocks  show  no  evidence  of  having  originated 
from  descending  waters.  This  theory  is  also  open  to  the  ser- 
ious objection  that  metallic  elements  would  be  deposited  by 
surface  waters  in  as  great  abundance  in  regular  sedimentary 
rock  strata  as  in  fissures.  There  is  ,  however,  some  evidence 
to  show  that  descending  water  from  rains  and  melted  snow, 
charged  with  atmospheric  gases,  do  enter  fissures  and  tend  to 
concentrate  the  metallic  elements.  This  fact  is  proven  by 
the  deposit  of  ores  on  the  down-stream  wall  of  fissures  in 
greater  abundance  than  elsewhere,  but  such  metallic  ele- 
ments appear  to  have  been  derived  from  the  eroded  surfaces 
of  mineralized  veins,  or  from  disintegrated  igneous  rocks  in 
the  vicinity  rather  than  from  the  sea  water. 

Many  mining  men  cling  to  the  descending  water  theory, 
and  the  local  enrichment  of  veins,  often  found  near  the 
permanent  water  level,  are  generally  believed  to  be  due  to 
concentration  of  the  metallic  elements  by  descending  waters, 
leached  from  minerals  above.  But  this  is  a  secondary  process, 
and  it  utterly  fails  to  prove  surface  waters  as  the  original 
source  of  the  metals  found  in  veins  and  cavities. 


182     PRACTICAL  GEOLOGY  AND  MINERALOGY 

(5)   What  Is  the  Sublimation  Theory? 

18.  According  to  this  popular  theory,  veins  are  mineral- 
ized by  volatilization  of  metallic  substances  within  the  earth. 
The    arising   metallic   vapors   coming   in   contact    with    the 
cooler  crust  above,  form  sublimates  or  crusts  of  the  metals 
within  the  veins,  which  may  later  assume  the  form  of  native 
metals.     Several  authorities  contend  this  is  the  true  solution 
of  the  origin  of  most  ore  deposits,  and  indeed  strong  evidence 
is  not  wanting  to  substantiate  this  theory.    The  admitted  fact 
of  the  occurrence  of  ore  bodies  within  veins  in  "chimneys," 
"shoots"  and  "pipes  of  ore"   is  difficult  to  explain  on  any 
other  hypothesis.     The   known   intense  heat  of  the  earth's 
interior,  the  proven  volatility  of  all  metals  at  high  tempera- 
tures, and  the  fact  that  metallic  vapors  condense  and  form 
sublimates    in    coming   in    contact    with    cool'  surfaces,    are 
additional  evidences  to  substantiate  this  theory. 

The  theory  of  sublimation  is  applied  to  all  the  so-called 
precious  metals,  as  having  been  deposited  within  the  open  and 
porous  sections  of  veins  previously  filled  with  gangue  min- 
erals. It  is  not  claimed,  however,  that  the  vein  filling  such 
as  quartz,  spar,  etc.,  are  themselves  deposited  by  sublimation. 

(6)   What  Is  the  Theory  of  Lateral  Secretion? 

19.  This  theory  is  based  upon  the  admitted  fact  that  all 
country  rock  contains  metallic  substances  in  finely  divided 
particles.     These   are   assumed   to   be   collected   by   waters, 
charged  with  atmospheric  gases,  circulating  through  the  more 
or  less  fractured  rocks  to  concentrate  the  metallic  elements 
in  cavities  or  porous  sections  of  lodes.     This  theory  is  reas- 
onable and  for  the  last  quarter  century  has  been  quite  genera- 
ally  accepted.     But  recently  the  trend  of  scientific  opinion 
has  turned  against  the  lateral  secretion  theory.     The  chief 


MINERAL  DEPOSITS 183 

objection  is  founded  on  the  insignificant  metallic  contents  of 
country  rocks  from  which  concentration  might  reasonably 
take  place,  and  if  metals  were  so  derived,  all  veins,  and  per- 
haps dikes,  should  be  uniformly  mineralized.  The  practical 
mining  man  knows  that  this  is  not  the  case. 

(7)    What  Is  the  Theory  of  Ascending  Waters? 

20.  This   is   a   most   popular   modern   theory.      In   its 
earlier  form  the  supposition  was  that  veins  are  formed  by 
minerals  dissolved  out  of  the  adjacent  rocks,  the  chief  portion 
of  which  is  derived  from  great  depth  and  deposited  by  hot 
waters  circulating  through  fissures.    The  modern  application 
of  this  theory  simply  undertakes  to  account  for  the  deposit  of 
metallic  elements  in  the  gangue  minerals  of  veins  previously 
formed   by   igneous  action.      It   is  well   known   that   heated 
mineral    waters    possess    great    solvent    properties,    and    the 
expansion  due  to  heat  and  pressure  below  causes  the  water 
charged  with  mineral  matter  to  rise  and  circulate  through  the 
portions  of  veins  offering  the  least  resistance.     As  the  solu- 
tions cool   in   their   upward   course,   the   metallic  burden   is 
deposited  in  the  gangue  matter.     The  presence  of  metallic 
mineral  deposits  in  the  vicinity  of  hot  springs  seems  to  con- 
firm this  theory,  although  such  hot  springs,  like  craters  of 
volcanoes,  do  not  have  metals  deposited  on  their  walls,  as 
both  fusions  and  solutions  must  cool  before  sublimation  or 
precipitation  can  be  effected. 

(8)     Theory  of  Replacement 

21.  This  is  the  most  modern  theory  advanced  and  has 
many  supporters.     It  is  somewhat  a  modification  of  the  Lat- 
eral Secretion  theory,  and  only  differs  from  it  in  the  supposi- 
tion that  the  particles  of  mineral  dissolve  out  of  the  country 
rock  have  substituted  in  their  place  mineral  matter  from  the 


184     PRACTICAL  GEOLOGY  AND  MINERALOGY 

solvents  circulating  in  the  vein  itself.  This  interchange  or 
substitution  of  mineral  matter  from  veins  for  those  leached 
out  of  the  wall  rock  is  assumed  to  continue  until  it  results  in 
a  deposit  of  ore.  Certain  irregular  ore  bodies  no  doubt  are 
thus  formed,  but  that  any  veins  are  so  mineralized  is  ex- 
tremely doubtful. 

What  Conclusions  May  Be  Drawn  From  These 
Theories? 

22.  From  this  apparent  conflict  of  opinion  amongst  the 
authorities,  it  might  be  thought  the  ordinary  mining  man  has 
little  hope  of  arriving  at  a  satisfactory  conclusion. 

Certain  principles,  however,  stand  out  boldly  as  a  result 
of  our  examination  of  these  several  theories  so  that  we  may 
sum  up  the  evidence  and  arrive  at  a  verdict.  The  following 
points  are  fairly  well  established: 

(1)  The  immediate  source  of  metallic  ores  is  within 
the  earth. 

(2)  Metallic  elements  are  everywhere  present,  but  re- 
quire to  be  concentrated  by  nature's  forces  before  workable 
ore  deposits  are  formed. 

(3)  Metallic  vapors  arising  from  the  earth's  interior 
are  either  absorbed  by  circulating  waters  or  deposited   by 
sublimation, 

(4)  The  open  and  porous  portions  of  veins  and  rocks 
are  mineralized  by  metallic  gases  and  by  solutions  circulating 
through  them. 

(5)  Surface   waters   charged   with    atmospheric   gases, 
precipitate  the  elements  from  hot  metallic  vapors  and  solu- 
tions to  form  ore  deposits. 

(6)  No  single  theory  can  be  applied  to  all  forms  of  ore 
deposits,  as  two  or  more  agencies  are  usually  present  and  act- 
ing to  concentrate  metallic  elements  into  ore  deposits. 


MINERAL  DEPOSITS.  185 

Ideal  Section  Illustrating  Origin  of  Ore  Deposits 

23.  It  is  difficult  to  draw  a  picture  representing  the 
crust  and  the  several  processes  heretofore  described, 
^•suiting  in  ore  deposits,  without  also  drawing  heavily  on 
the  imagination.  However  we  have  a  few  demonstrated 
facts  to  guide  us,  and  with  these  as  a  skeleton  we  may  build 
upon  it  a  framework  in  accordance  with  the  principal  theories 
of  ore  deposition  heretofore  described. 

Fig.  47  represents  a  section  of  the  earth's  crust  showing 
the  three  Zones.  The  Oxide  extending  from  the  surface  to 
water  level,  represented  by  the  bed  of  the  water  course  at  2. 
In  this  Zone,  as  its  name  indicates,  the  rocks  are  fractured 
and  fissured  to  such  an  extent  that  the  surface  waters  and 
atmospheric  gases  circulate  throughout  them  down  to  the 
water  level.  The  Sulphide  Zone  is  seen  extending  from  the 
Oxide  at  B  to  the  Flowage  at  C.  In  this  Zone  the  fractures 
are  smaller  and  the  earth's  heat  greater.  The  Molten  Zone 
is  seen  extending  from  C  to  D.  Here  the  temperature  and 
pressure  are  great,  and  fractures  hair  like.  A,  B,  C,  D, 
represents  a  Fissure  vein  in  process  of  filling.  The  lines  1,  2, 
16,  17  and  18  represent  channels  through  which  surface 
waters  and  atmospheric  gases  find  their  way,  dissolving  out 
the  soluble  mineral  elements  and  depositing  their  burden 
into  the  great  central  trunk  vein.  The  lines  at  2,  3,  4,  5,  12, 
13,  14  and  15,  show  assumed  channels  for  the  passage  of 
warm  water  solutions,  also  leading  to  the  main  trunk.  The 
lines  6,  7,  8,  9,  10  and  11  also  show  theoretical  channels  for 
vaporized  waters  and  metallic  gases  generated  by  heat  and 
pressure,  which  by  reason  of  their  lesser  specific  gravity  and 
eruptive  forces  there  present  take  an  upward  course  through 
the  Sulphide  and  into  the  Oxide  Zone.  These  coming  in 
contact  with  cooler  mineral  solutions  from  above  would  have 


186    PRACTICAL  GEOLOGY  AND  MINERALOGY 


.'x .x; 

•<•  '  x.1  x.  x.'  >i'  K.'ii'X'. x;*;X. . 

'     '        -  > 


Fig.  47.     Ibeal  Section  Illustrating  Genesis  of  Ore  Deposits. 


MINERAL  DEPOSITS  187 

their  metallic  contents  deposited  by  sublimation  or  precipita- 
tion in  the  more  open  and  porous  gangue  minerals  of  the  vein 
above.  On  the  contrary,  the  surface  waters  charged  with 
dissolved  minerals  in  meeting  an  ascending  current  would 
tend  to  precipitate  their  metallic  burden  also,  and  these  pro- 
cesses continued  throughout  vast  ages  result  in  deposits 
of  ore. 

The  shaded  section  of  vein  at  B  represents  the  "Zone  of 
Secondary  Enrichment,"  resulting  from  the  leaching  of  ores 
above  and  the  precipitation  of  their  metallic  burden  at  the 
water  level.  Within  the  vein  above  the  water  level  occur 
oxides,  sulphates,  chlorides  and  carbonates  of  the  metals, 
which  result  from  the  alteration  of  sulphides  by  coming  in 
contact  with  the  oxygen  of  the  atmosphere  and  with  the 
descending  waters. 

Below  the  water  level  all  minerals  contained  in  veins  are 
sulphides.  Below  point  C,  or  in  the  Flowage  Zone,  we  may 
only  guess  whether  there  would  be  a  different  ore,  or  no  ore 
at  all,  since  no  shafts  have  as  yet  penetrated  this  Zone. 
However,  it  seems  certain  with  the  known  increase  of  tem- 
perature that  metallic  elements  would  likely  be  in  a  molten 
or  gaseous  state. 

Laboratory  experiments  have  demonstrated  the  principles 
upon  which  the  theories  relating  to  ore  deposits  are  based, 
and  since  the  same  unchanging  laws  prevail  everywhere,  we 
are  reasonably  sure  that  similar  reactions  are  taking  place  in 
nature's  vast  laboratory  within  the  earth.  At  best,  man  can 
only  imitate  nature,  and  it  is  possible  that  there  are  agencies 
and  processes  as  yet  undiscovered  and  which  if  fully  under- 
stood would  make  clear  many  things  in  regard  to  the  forma- 
tion of  ore  deposits  that  are  now  somewhat  clouded. 


188    PRACTICAL  GEOLOGY  AND  MINERALOGY 

What  Is  Nature's  Preparation  for  Mineral  Deposits? 

24.  We  behold  a  plan  or  design  in  everything  in  nature, 
and  the  formation  of  ore  deposits  is  no  exception  to  the  gen- 
eral rule.     It  must  be  apparent  that  if  the  earth  were  one 
solid  uniform  body  no  mineral   deposits  could   be   formed. 
Under  the  subject  Geology  we  learned  that  countless  ages 
were  required  to  prepare  the  earth  for  man,  and  it  is  evident 
that  the  same  "Supreme  Intelligence"  has  made  a  somewhat 
similar  preparation  for  the  reception  of  ore  deposits.     Earth 
movements  have  fractured  the  crust,  producing  fissures  and 
cavities  in  which  to  concentrate  metallic  minerals.     Complex 
faulting  and  igneous  eruptions  have  permitted  metallic  vapors 
from  below  to  penetrate  these  open  spaces  in  the  crust,  which 
fissures  also  serve  as  channels  for  the  circulation  of  under- 
ground waters  to  concentrate  the  metallic  elements  into  ore 
deposits.      These   processes   have   continued   throughout   the 
ages  and  doubtless  will  not  cease  until  the  end  of  time. 

How  Are  Mineral  Deposits  Classified? 

25.  Mineral  Deposits  are  so  varied  in  form  and  origin 
that  it  has  been  difficult  for  the  authorities  to  adopt  a  standard 
classification.     Many  different  schemes  have  been  proposed, 
but  it  is  generally  agreed  that  the  only  natural  basis  of  classi- 
fication is  that  of  origin.     If  we  know  the  natural  agencies 
that  have  caused  a  mineral  deposit  we  are  able  to  estimate  its 
probable  value  and  extent,  and  thus  be  able  to  formulate  a 
practical  plan  for  removing  the  mineral. 

For  example:  If  a  mineral  deposit  has  all  the  characteris- 
tics of  a  fissure  vein  filling,  its  future  may  be  forecast  with  a 
fair  degree  of  accuracy  by  applying  the  rules  governing  fissure 
veins. 


MINERAL  DEPOSITS  189 

Clasification  of  Mineral  Deposits 

I.  REGULAR  DEPOSITS. 

(a)  BEDS  (STRATIFIED  DEPOSITS). 

(1)  Sedimentary   Deposits. — Residue    from   Evapora- 
tion. 

(2)  Placer   and    Beach    Deposits. — Mechanically   de- 
posited by  water. 

(3)  Coal  Measures. — Vegetable  matter  enclosed  and 
compressed  by  Stratified  Rocks. 

(4)  Petroleum. — Buried  Organic  Matter,  Condensed 
and  Refined. 

(b)  VEINS  (UNSTRATIFIED  DEPOSITS). 

( 1 )  Fissure  Veins. — Regular  Walls  of  Similar  Rocks. 

(2)  Contact  Veins. — Unlike  Walls  of   Igneous   and 
Aqueous  Rocks. 

(3)  Gash  Veins. — Filled  Surface  Cracks,  Irregular  in 
Strike  and  Dip. 

(4)  Segregated     Veins. — Irregular     Form.       Follow 
Folds  of  Enclosing  Rocks. 

II.  IRREGULAR     DEPOSITS     (Without     Walls  or  Definite 
Definite  Form). 

( 1 )  Chamber  Deposits. — Filled  Cavities  of  Uncertain 
Origin. 

(2)  Impregnation   .  and      Stockwork.  —  Mineralized 
Veins  and  Wall  Rock. 

(3)  Fahlbands.— Mineralized  Rock  Strata. 

The  above  outline  includes  all  the  deposits  of  especial 
interest  to  the  mining  man,  and  they  will  now  be  considered 
in  the  order  named : 


190    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Beds  or  Stratified   Deposits — What  Are  They? 

26.  The  origin  of  mineral  deposits  occurring  in  regular 
layers  between  sedimentary  rocks  is  not  difficult  to  under- 
stand.   They  all  lie  parallel  with,  and  conform  to,  the  bend- 
ing and   folding  of  the  enclosing  rocks,   which   fact  often 
throws  the  deposits  into  arches  or  saddles,  called  Anticlines, 
while  the  lower  folds  form  troughs  or  Sinclines.     (See  Figs. 
29  and  50.)     Such  deposits  were  all  formed  during  the  same 
period   as   the   enclosing   rocks,    and   are   of   surface   origin 
entirely.     Stratified  Deposits  can  have  no  regular  walls  like 
veins,  so  the  upper  stratum  is  called  a  "roof"  and  the  lower 
stratum  is  called  the  "floor." 

How  Are  Bedded  Deposits  Formed? 

27.  Such  deposits  are  either  formed  by  sediments  washed 
down  from  the  heights  like  sedimentary  rocks,  or  from  the 
evaporation   of   the   water    from   mineral   solutions,   leaving 
behind  the  solid  mineral  elements.     Salt-beds  are  formed  in 
basins,  formerly  a  part  of  the  ocean.     The  waters  vaporized 
and  passed  into  the  atmosphere,  leaving  the  residue  of  salt 
chemically  known  as  Chloride  of  Sodium.    These  beds  when 
covered  up  for  ages  and  brought  into  contact  with  the  heat  of 
the  earth,  or  igneous  rocks,  are  crystallized  into  the  mineral 
Halite.    Some  limestones  and  gypsums  are  thus  formed  from 
dissolved  mineral  matter,  washed  into  basins  by  waters  dry- 
ing up  and  leaving  mineral  beds  behind,  which  may  be  later 
crystallized. 


MINERAL  DEPOSITS  19! 

What  Are  Placer  Deposits? 

28.  There  are  three  kinds  of  Placer  Deposits,  differing 
only  in  occurrence,  which  are  concentrated  mechanically  by 
the  action  of  water  on  the  gravity  principle,  viz: 

(a)  Stream  Deposits, 

(b)  Ancient  River  Deposits, 

(c)  Beach  Deposits. 

The  metals  usually  found  in  placers  are  Gold,  Tin  and 
Platinum,  these  only  being  able  to  resist  the  erosive  and  cor- 
rosive elements.  The  high  specific  gravity  of  these  metals 
favor  their  concentration  into  beds,  the  lighter  elements  wash- 
ing off  leaving  the  heavier  behind.  Some  recent  writers  claim 
that  placer  minerals  are  formed,  in  part  at  least,  from  metal 
solutions.  (See  Par.  32). 

29.  Stream    Placers    are    those    found    in    present    day 
water  courses  and  are  of  comparatively  recent  origin,  dating 
from  the  Tertiary  Age.     Streams  in  all  mineralized  districts 
contain  more  or  less  placer  minerals  in  the  form  of  nuggets, 
grains  or  fine  metallic  flakes.  These  have  been  carried  to  their 
present  position  by  moving  waters  or  glaciers,  from  eroded 
outcroppings  of   mineralized    veins,    or    from   disintegrated 
igneous  rocks. 

The  character  of  the  placer  metal  is  said  to  indicate  its 
origin.  That  is,  if  the  native  metal  is  coarse  grained  and 
rough  edges,  it  indicates  the  source  is  near  at  hand  in  well 
mineralized  ledges;  but  if  the  metallic  particles  are  fine  and 
flaky  with  well  rounded  edges,  it  indicates  the  metallic  par- 
ticles have  traveled  far,  and  their  origin  is  possibly  due  to  the 
action  of  Glaciers.  (See  Glaciers.) 

The  placer  metals  are  usually  found  mixed  throughout 
the  pebbles  and  sands,  but  the  richer  deposits  are  found  near 


192     PRACTICAL  GEOLOGY  AND  MINERALOGY 

bedrock.     The  most  favorable  catchment  basins  are  formed 
where  the  stream  is  somewhat  level. 

In  Fig.  72  is  shown  an  ideal  placer  deposit.  The  bed- 
rock A-A  is  an  upturned  schist,  into  which  are  formed  cavit- 
ies that  catch  the  heavier  metallics  that  sift  down  through  the 
sand  and  gravel  of  the  stream  bed.  At  B  is  what  is  called  a 
"pot-hole,"  which  acts  as  a  trap  to  catch  metallic  grains. 
When  the  rock-strata  is  tilted  up-stream,  it  makes  a  most 
effective  catchment  basin.  A  stratum  of  clay  in  a  stream 
placer  often  collects  and  holds  the  concentrated  metals,  but 
makes  their  separation  from  the  clay  very  difficult  and  expen- 
sive. It  is  evident  that  placer  metals  cannot  be  deposited  in 


Fig.  72.  Gold  Placer  Deposit  in  Cavity  of  Upturned  Bed.    Rock  Schists. 

swiftly  moving  currents,  but  where  eddies  form  or  when  a 
stream  changes  its  channel  the  old  bed  is  where  workable 
deposits  are  usually  found. 

What  Is  the  Origin  of  Ancient  River  Deposits? 

30.  These  are  found  throughout  California,  often  in 
the  tops  of  the  hills  and  mountains  and  sometimes  capped  by 
volcanic  rocks  from  Tertiary  eruptions.  The  presence  of 
organic  matter  in  the  form  of  driftwood  in  such  deposits  is 
positive  proof  that  they  were  ancient  river  channels,  which 
have  either  since  been  pushed  up  or  the  adjacent  country  has 


MINERAL  DEPOSITS  193 

sunken.  Fig.  48  shows  an  Ancient'  River  Placer.  The 
dotted  line  represents  the  original  contour  of  the  country, 
the  basalt  capping  is  assumed  to  have  been  formed  by  the 
flow  of  molten  lava  which  diverted  the  river  course  else- 
where. Subsequent  earth  movements  uplifted  the  beds,  or 
depressions  were  formed  on  each  side,  leaving  the  Ancient 
River  Deposits  high  and  dry. 

Sometimes  an  Ancient  River  Bed  is  depressed  and  cov- 
ered up  hundreds  of  feet  by  sedimentary  or  eruptive  matter, 
making  it  necessary  to  sink  shafts  or  drive  tunnels  to  work 
such  placers,  as  in  lode  mining. 

Fig.  48 


-ANCIENT     GOLD-BEARING      RIVER      BEDS,      TABLE 
MOUNTAIN,  CALIFORNIA. 

How  Are  Beach  Placers  Formed? 

31.  Beach  Placers  are  found  along  the  Pacific  Coast  of 
of  North  America,  the  most  noted  being  at  Nome,  Alaska, 
where  the  upturned  strata  of  slate  and  schist  carry  gold- 
bearing  veinlets,  while  the  dikes,  or  cross-veins,  act  as  dams 
or  "pot-holes"  to  catch  the  gold.  Fig.  49  shows  a  section  of 
Nome  Beach  Deposits.  T-he  source  of  this  gold  is  inland  and 
not  seaward.  It  was  washed  down  by  floods  or  glaciers, 
while  subsequent  earth  movements  possibly  brought  the  gold 
in  contact  with  the  ocean  tidal  waves,  to  concentrate  it  into 
Beach  Placers. 

In  these  Beach  Placers  the  gold  is  concentrated  by  the 
waves.  The  incoming  tidal  waves  are  counteracted  by  con- 


194    PRACTICAL  GEOLOGY  AND  MINERALOGY 

tact  with  the  shore-line,  but  the  undertow  of  the  receding 
tidal  waves,  assisted  by  gravity,  carry  the  lighter  particles 
seaward.  This  leaves  the  heavier  particles  concentrated 
behind  into  placer  beds,  which  are  often  of  remarkable 
richness. 

What  Is  the  Origin  of  Nuggets  in  Placers? 

32.  The  origin  of  gold  nuggets  found  in  placers  has 
long  been  somewhat  of  a  mystery,  and  inasmuch  as  this 
question  has  an  important  bearing  on  placer  mining,  it 
deserves  some  consideration  here. 


Fig.  49.      Section  Representing  Nome,  Alaska  Beach  Placers. 

So  far  as  the  origin  of  fine  grain  and  flake  placer  gold  is 
concerned,  the  problem  is  quite  simple.  Gold  is  obtained 
from  "free  milling"  ores  and  from  gulches  below  such  mines 
by  panning,  as  from  placer  beds,  which  is  convincing  evi- 
dence that  the  origin  of  such  placer  gold  is  traceable  to  the 
eroded  mineralized  veins  at  higher  levels.  However,  the 
existence  of  coarse  grains  of  gold  and  nuggets  in 
placers,  often  weighing  from  an  ounce  to  several 
pounds,  is  not  so  easily  explained.  It  is  contended 
that  such  nuggets  result  from  the  decomposition  of 
gold-bearing  quartz.  The  silicious  matter  being  more 
soluble  than  the  gold  content  it  disintegrates,  leaving  a 


MINERAL  DEPOSITS 195 

skeleton,  or  honey-combed  structure.  This  contains  tiny 
wires  of  metal,  which  moving  rocks  crush,  and  the  malleable 
gold  is  consolidated  into  the  form  of  nuggets.  The  fact  that 
coarse  placer  gold  often  has  little  particles  of  quartz  adhering 
to  it  seems  to  confirm  this  old  theory.  Still  this  explanation 
is  not  altogether  satisfactory,  and  some  recent  writers  have 
raised  serious  objections  to  this  view.  They  point  out  that 
there  is  a  directly  opposite  tendency  in  alluvial  gold  being 
ground  into  fine  flakes  and  powder  in  moving  from  the 
heights  to  the  basins  below.  It  is  also  pointed  out  that  gold 
in  lodes  is  alloyed  with  silver  ranging  from  5  to  35  per  cent, 
while  the  gold  in  placers  is  often  almost  chemically  pure. 
Those  who  hold  to  the  old  theory,  endeavor  to  explain  that 
silver,  being  more  soluble  than  gold,  is  dissolved  out  by 
acids  and  alkalies  in  water  and  the  atmosphere,  leaving  the 
gold  in  the  refined  state.  Laboratory  experiments,  however, 
do  not  bear  out  this  assumption,  as  silver  is  very  difficult  to 
part  from  an  alloy  with  gold,  except  when  in  finely  divided 
particles. 

The  existence  of  large  gold  crystals  within  placers  can- 
not be  satisfactorily  explained,  except  that  they  were  crys- 
tallized within  the  placer  beds  themselves.  We  have  seen 
that  crystals  are  formed  by  two  processes, — fusion  and 
solution.  If  we  assume  such  crystals  were  formed  within 
lodes,  their  crystal  form  would  surely  be  destroyed  by  ero- 
sion and  corrosion  in  traveling  from  such  decomposed  vein 
outcrop  to  placer  beds  often  many  miles  distant. 

These  recent  writers  contend  that  Gold  Nuggets  and 
crystals  are  formed  within  the  placer  beds  by  a  sort  of  min- 
eral growth.  The  gold  is  dissolved  by  combined  action  of 
alkalies  and  acids,  and  the  metal  burden  being  precipitated 
by  natural  reagents  to  form  metallic  gold  around  a  nucleus. 


1%    PRACTICAL  GEOLOGY  AND  MINERALOGY 

This  continued  growth  by  accretion,  or  addition  of  precipi- 
tated gold,  is  believed  to  form  the  crystals  and  nuggets 
found  in  placers  today.  If  it  is  admitted  that  gold  is  ren- 
dered soluble  by  the  natural  reagents  in  surface  waters,  it  is 
reasonable  to  conclude  that  the  origin  of  placer  nuggets  and 
gold  crystals  is  within  the  placers  themselves  and  that  the 
metallic  elements  are  concentrated  from  vast  areas. 

Coal  Measures — What  Are  They  and  How  Formed? 

33.  Coal  is  not  a  true  mineral  because  it  has  a  variable 
composition,  but  inasmuch  as  it  belongs  to  the  mineral  king- 
dom it  may  very  properly  be  classed  as  a  mineral  deposit. 

Coal  Measures  occur  in  stratified  beds  and  differ  from 
other  mineral  deposits  in  origin.  These  have  been  formed 
from  vegetable  matter  like  mosses,  lichens,  shrubs  and  even 
whole  primitive  forests  which  have  been  submerged,  in  the 
processes  of  the  ages,  beneath  the  seas  and  covered  with  sedi- 
mentary rocks  at  varying  depths.  Coal  is  usually  found  in 
a  sandstone  formation  with  shale  or  slate  for  roof  and  floor, 
which  are  probably  impurities  driven  out  of  the  organic 
matter  by  pressure  from  above  and  baked  by  the  earth's  heat. 
Coal  measures  usually  lie  horizontal,  but  earth  movements 
have  often  tilted  up  the  beds  at  different  angles.  Instances 
are  found  in  the  Rocky  Mountain  region  where  the  intrusion 
of  an  igneous  dike  has  changed  soft  coal  into  anthracite. 
(See  Carboniferous  Age.) 

Petroleum — What  Is  It  and  How  Formed? 

34.  Petroleum    varies   somewhat    in    composition,    like 
coal.     The  word  literally  means  "rock  oil"  and  the  name 
"Coal  oil"  that  was  first  applied  to  Petroleum  is  a  misnomer, 
as  it  is  not  a  product  of  coal,  although  often  closely  associated 
with   it.     The  origin   of    Petroleum   and   natural   gas   has 


MINERAL  DEPOSITS 197 

puzzled  the  geologist  and  chemist  from  the  date  of  their 
discovery.  Chemists  have  been  able  to  extract  Petroleum 
from  coal  and  also  from  limestone,  and  in  some  countries 
shale  is  ground  up  and  the  oil  extracted  on  a  commercial 
scale.  A  product  closely  resembling  petroleum  has  been 
extracted  from  decomposing  animal  bodies  by  distillation. 
These  facts  point  clearly  to  the  source  of  Petroleum  as  a 
product  of  organic  matter,  both  animal  and  vegetable,  and 
on  this  scientists  are  now  fairly  well  agreed.  The  processes 
by  which  Petroleum  is  produced  in  nature's  vast  under- 
ground laboratory  are  superior  to  anything  known  to  man 
and  have  been  in  operation  throughout  vast  ages. 

The  highest  quality  of  Petroleum  is  found  at  consider- 
able depth  in  the  Devonian  rocks,  but  it  occurs  in  greater 
abundance  in  the  rocks  of  the  Carboniferous  Age.  As  these 
were  known  to  be  ages  of  rank  vegetation  and  abundant 
animal  life,  we  have  additional  proofs  of  organic  origin  of 
Petroleum.  The  heavy  California  Oils  occur  in  the  Ter- 
tiary Rocks,  just  as  low  grade  coals  occur  in  the  more 
recent  formations. 

The  great  oil  bearing  strata  within  the  earth  are  always 
in  regular  beds  of  slate  and  cavernous  limestones.  The  fine 
grained  slates  act  as  a  roof  to  catch  and  hold  the  oil  and 
gases  generated  below. 

Fig.  50  shows  a  section  of  a  California  Oil  Field,  the  oil 
stratum  lying  between  shale  strata,  which  follow  the  folia- 
tion of  the  enclosing  rocks. 

The  Anticlines  are  shown  at  A  and  B.  At  C  is  shown 
the  S incline,  the  great  natural  reservoir  for  oil  and  wells 
drilled  at  such  points  usually  prove  the  most  productive. 


198    PRACTICAL  GEOLOGY  AND  MINERALOGY 

At  the  extreme  left  is  shown  the  outcrop  of  oil  sand.  Inex- 
perienced oil  miners  often  put  down  wells  where  oil  appears 
on  the  surface,  and  the  result  is  usually  a  "dry  hole." 

Petroleum  is  lighter  than  water,  hence  it  rises  and  col- 
lects under  the  saddles,  or  anticlines,  while  the  surplus  water 
leaks  out  through  fissures  under  the  troughs  or  sinclines,  and 
in  this  way  the  oil  is  purified.  In  a  few  California  oil  fields 
the  rock  enclosing  the  oil  strata  have  been  pushed  up  and 
formed  into  basins  similar  to  Ancient  Placer  Beds  shown  in 
Fig.  31  and  Fig.  51. 


Fig.  50.     Ideal  Section  Showing  California  Oil  Field. 

Unstratined  Deposits 

35.  Before  taking  up  the  subject  of  Ore  Deposits,  it 
will  be  well  to  thoroughly  understand  the  difference  be- 
tween a  mineral  and  an  ore,  as  well  as  the  distinction 
between  ore  in  a  vein,  and  the  vein  itself. 

What  Constitutes  An  Ore? 

An  ore  is  defined  to  be  any  mineral,  or  aggregation  of 
minerals  from  which  a  metal  may  be  recovered  at  a  profit 
over  and  above  the  cost  of  extraction.  From  this  it  is  seen 
that  the  element  of  profit  determines  what  is  really  ore. 


MINERAL  DEPOSITS 


199 


An  ore  of  pure  minerals  is  unusual.  It  is  possible  for  one  to 
have  a  vein  in  which  pure  mineralogical  specimens  occasion- 
ally occur  and  yet  not  have  an  ore,  on  account  of  such  min- 
erals occurring  in  small  pockets.  Likewise  a  vein  carrying 
a  certain  percent  of  metal  in  one  section  may  be  an  ore,  and 
in  another  section  an  equal  proportion  of  the  same  minerals 
may  not  be  an  ore  at  all,  owing  to  unfavorable  conditions 
making  the  cost  of  recovering  greater  than  the  value  of  the 
metals  extracted.  For  example,  Pyrrhotite  containing  two 
per  cent  copper,  if  so  situated  that  it  can  be  economically 
mined  and  reduced,  would  constitute  an  ore,  while  the  same 

Fig.  51. 


ANTICLINAL  AND  SYNCLINAL  FOLDS. 

percentage  of  metal  in  pyrrhotite,  remote  from  railroad  and 
smelter,  or  with  unfavorable  conditions  for  mining  and  ex- 
tracting, would  be  consigned  to  the  "waste  dump." 

Minerals  formerly  not  considered  ores  on  account  of 
expensive  methods  are  today,  with  improved  processes  and 
scientific  treatment,  valuable  ores.  The  mineral  Bauxite  is 
now  a  valuable  ore  of  Aluminum,  but  a  century  ago  Alum- 
inum metal  was  unknown,  hence  Bauxite  was  simply  "rock." 
So  also  what  we  regard  as  common  clay  today,  with  im- 
proved scientific  methods  of  the  future,  may  become  a 
valuable  Aluminum  ore. 


200    PRACTICAL  GEOLOGY  AND  MINERALOGY 

36.  High  Grade  is  a  term  used  to  denote  a  high  per- 
centage of  metal,  depending  somewhat  on  the  metal  content. 
When  only  a  small  percentage  of  metal  is  present,  or  low 
values,  it  is  said  to  be  lean  or  low  grade. 

An  ore  containing  one  per  cent  gold  would  be  extremely 
rich,  and  hence  properly  named  high  grade,  but  one  per  cent 
copper,  or  lead,  would  be  low  grade,  or  no  grade  at  all,  even 
with  the  most  modern  methods  in  mining  and  extracting. 

Twenty-five  years  ago  iron  ores  of  Lake  Superior  region 
carrying  less  than  60%  were  considered  'low  grade,"  but 
with  modern  methods  ores  carrying  40%  kon  are  now  con- 
sidered valuable.  In  ore  of  the  "precious  metals,"  the 
gangue  minerals — like  iron,  lime  and  silica,  constitute  the 
body  of  an  ore,  and  the  precious  metals  are  usually  present 
only  in  finely  divided  particles.  So  in  order  to  determine 
the  class  of  an  ore,  a  general  average  must  be  taken  of  that 
portion  of  the  vein  material  that  must  be  removed  in  ordinary 
mining.  Sometimes  it  is  necessary  to  take  average  samples 
clear  across  from  wall  to  wall  in  order  to  estimate  the  ton 
value  of  an  ore  body.  Failure  to  observe  this  rule  is  respons- 
ible for  more  mistakes  and  failures  in  mining  than  any  other 
cause.  Another  common  error  of  the  inexperienced  is  to 
conclude  that  every  part  of  a  ledge  is  equally  good,  or 
barren.  Such  mistakes  arise  from  the  belief  that  the  vein 
is  mineralized  when  formed,  whereas  ore  occurs  in  "shoots," 
which  in  appearance  do  not  differ  from  the  "lean"  or  barren 
portion  of  the  vein.  (See  Ore  Shoots,  Par.  46). 


MINERAL  DEPOSITS 


What  Physical  Conditions  Influence  Ore  Deposits? 

37.  Ore  being  an  aggregation  of  minerals  collected 
from  the  great  earth  mass,  it  must  be  apparent  that  certain 
physical  conditions  favor  the  concentration  of  metallic  par- 
ticles to  form  ore  deposits.  These  conditions  are  somewhat 
varied,  but  the  following  exercise  the  greatest  influence,  viz: 

(1)  Dikes, 

(2)  Faults, 

(3)  Wall  Rocks. 

(1)  Dikes  of  igneous  rocks  like  porphyry,  diorite,  etc., 
are  seldom  mineralized  and  therefore  unimportant  in  them- 
selves.    But  when  they  occur  in  contact  with  or  adjacent  to 
regular  veins  they  produce  the  morphological  changes  highly 
favorable  to  vein  mineralization. 

(2)  Faults  produced   by  earth  movements   may  show 
themselves  in  sharp  cuts  extending  great  distances,  or  they 
may  occur  as  a  mass  of  fractured  material.     Regions  subject 
to  earthquakes  are  most   extensively   faulted,   and  similarly 
such  regions  contain  the  most  valuable  deposits  of  the  prec- 
ious   metals.      The    open    porous    condition    resulting    from 
faulting  permit  the  metallic  vapors  and  mineral  solutions  to 
enter  such  cavities  and  deposit  their  metallic  matter. 

(3)  Wall  Rock,  often  affects  both  the  vein   and  the 
filling.     A  tough  enclosing  rock  may  narrow  a  vein  to  a 
mere  seam,   and   a  soft  wall   rock  may  permit   the  vein  to 
widen  out.     Soluble  rocks  like  limestone  and  dolomite  may 
give  up  some  of  their  substances,  and  have  them  replaced  by 
mineral  solutions  circulating  through  the  vein  fissures.    Vein 
matter  that  is  compact  and  continuous  in  one  rock,  passing 
into  another  strata,  may  split  up  into  stringers  so  as  to  prove 
unprofitable. 


202    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Veins — What  Are  They? 

38.  Feins  are  faults  or  fissures  in  rock  strata  filled  with 
mineral  matter.     A  vein  is  made  up  of  three  parts,  viz: 

( 1 )  The    open    fissure,    which    may    be    clean-cut,    or 
simply  a  shattered  zone. 

(2)  The  gangue,  or  more  or  less  valueless  material, 
constituting  the  filling. 

(3)  The  Ore,  which  only  occurs  in  places  within  the 
vein. 

Veins  vary  in  width  from  an  inch  to  many  feet  and  from 
a  few  hundred  feet  to  many  miles  in  length.  A  vein  differs 
from  a  Bed  (See  Par.  24)  in  that  veins  are  unstratified  and 
were  formed  after  the  rock  strata  had  hardened,  so  as  to 
permit  faulting  and  fissuring. 

Veins  differ  from  Dikes  in  that  they  are  filled  in  suc- 
cesive  stages — a  sort  of  mineral  growth — while  Dikes  are 
fissures  filled  with  igneous  rocks  at  a  single  eruption,  and 
therefore  of  uniform  structure.  Dikes  have  their  walls 
burned  and  baked  by  the  heat  from  the  eruptive  matter. 
Veins  are  softer,  easily  fractured  and  oxidize  rapidly,  while 
Dikes  are  hard  and  decompose  more  slowly  than  the  enclos- 
ing rocks.  (See  Fig.  52.) 

39.  A  Lode  is  a  more  general  term  than  Vein,  and  this 
is  used  to  designate  any  fissure  or  mineralized  country  rock. 
As  used  in  the  U.  S.  Mining  Laws,  the  term  Lode  applies  to 
any  mineralized  Zone  or  Belt  lying  within  boundaries  clearly 
separated  from  neighboring  rocks. 

40.  A   Mineral  Belt   is  a  section  of  country  through 
which  run  a  series  of  parallel  veins  having  a  common  origin. 


MINERAL  DEPOSITS  203 

The  "Mother  Lode"  in  California  lies  in  a  Mineral  Belt 
about  fifty  miles  wide  and  nearly  one  hundred  miles  in 
length. 

41.  Country  Rock  is  a  term  used  to  designate  the  rock 
which  encloses  a  vein  or  bed.     (See  Fig.  52.)     When  the 
vein  varies  from  the  vertical  or  horizontal,  the  wall  rock 
forming  the  roof  is  called  the  Hanging  Wall,  and  that  form- 
ing the  floor  is  called  the  Foot  Wall. 

42.  Strike  is  the  extension  of  a  vein  or  lode  in  a  hori- 
zontal line.     In  other  words,  it  is  the  course  or  trend  of  the 

Fig.  52 


Shearaoe 

Zone        Quarrz  fisures 
and  oay  streak. 

A  composite   vein. 

vein,   usually  conforming  to  or  running  parallel  with   the 
course  of  the  hills  or  mountains. 

43.  Dip  is  the  term  .used  to  designate  the  angle  a  vein 
makes  with  the  horizon  in  its  downward  course.  Fig.  53 
shows  the  methods  of  measuring  Dip.  From  the  horizontal 
to  the  vertical  is  90  degrees,  making  what  is  called  a  Quad- 
rant, or  quarter  circle.  A  vein  forming  a  one-third  angle 
from  the  horizontal  would  be  30  degrees  Dip ;  one-half  pitch 
would  be  45  degrees  Dip,  and  so  on  as  shown  in  the  scale. 


204    PRACTICAL  GEOLOGY  AND  MINERALOGY 

Dip  is  sometimes  stated  in  per  cent  measured  from  the  verti- 
cal line.  Thus  one-fourth  incline  from  the  vertical  would  be 
termed  25%  Dip,  one-half  50%  Dip,  etc.,  as  shown  in 
Fig.  53. 

The  Outcrop  of  a  vein  is  what  appears  on  the  surface. 
Sometimes  a  vein  is  harder  than  the  wall  rocks  and  will 
stand  out  boldly,  or  some  portion  of  the  vein  may  be  hard 
and  other  parts  soft,  due  to  difference  in  fracturing  and 
cross  fissuring.  When  a  vein  contains  soft  and  soluble 


Fig.  53.     Illustrating  Dip  Veins. 

matter  it  may  be  worn  away  so  there  is  no  outcrop  at  all,  and 
in  that  case  it  is  said  to  be  a  blind  lead.  Often  such  decom- 
posed veins  may  be  traced  by  stains  imparted  to  the  country 
rock  along  the  "strike."  Oxide  iron  gives  a  yellowish  or 
brownish  stain,  but  copper  carbonates  impart  a  greenish  or 
bluish  stain.  This  decomposed  stained  ledge  matter  is  called 
by  miners  a  "Gossan"  or  "blossom,"  and  often  contains  free 
gold,  or  the  oxides  and  carbonates  of  lead,  copper,  etc. 

45.     A  Horse  is  a  miner's  term  to  designate  fragments 


MINERAL  DEPOSITS 


205 


of  wall  rock  included  within  vein  matter.  The  country 
rock  may  become  fractured  so  that  the  vein  in  the  process  of 
formation  enclosed  a  fragment  of  wall  rock  which  became 
detached,  or  a  rock  fragment  may  be  forced  into  the  vein 
after  it  is  formed.  In  either  case  the  vein  is  split  into  one  or 
more  parts.  Fig.  54  shows  "horses"  as  they  occur  in  a 
Colorado  mine;  the  light  colored  portion  represents  the  true 


Fig.  54.     Horses  in  Fissure  Vein,  San  Juan  Region,  Colorado. 

vein  matter,  and  the  enclosed  matter  constitutes  the  " horses." 
It  is  not  unusual  for  a  vem  to  branch  and  come  to  the  sur- 
face in  a  system  of  parallel  veins,  all  in  rocks  of  a  similar 
age,  but  where  a  vein  splits  in  its  downward  course  to  form 
"horses,"  as  shown  in  the  lower  portion  of  the  figure,  it  is 
an  unfavorable  indication  and  is  often  a  slur  on  the  mine  or 
prospect. 


206    PRACTICAL  GEOLOGY  AND  MINERALOGY 

What  Are  Ore  Shoots? 

46.  Veins  are  often  perfect  in  form  and  structure,  but 
imperfect  in  mineralization,  or  they  may  be  absolutely  bar- 
ren. When  ore  occurs  in  a  vein  it  is  usually  irregular  in 
shape  and  extent.  In  ideal  veins,  and  in  the  best  mines,  ore 
is  found  in  certain  sections  of  veins,  while  other  portions  of 
the  same  vein  may  be  imperfectly  mineralized,  or  entirely 
valueless.  Those  portions  or  sections  of  a  vein  carying  "Pay 
Ore"  are  called  ore  shoots  (or  chutes),  also  called  Pipes  of 
Ore,  from  their  pipe-like  shape.  A  common  name  amongst 
miners  is  Ore  Chimney,  which  name  applied  by  those  who 
believe  that  all  ore  bodies  are  formed  within  veins  by 
metalic  vapors  arising  from  the  earth's  interior  through  open 
vents  similar  to  the  movement  of  smoke  through  a  house 
chimney.  While  it  is  true  that  there  are  many  ore  bodies  to 
which  the  name  "chimney"  is  appropriate,  yet  for  ore  bodies 
formed  by  the  deposition  of  metallic  elements  from  circulat- 
ing solutions  the  name  Shoot  is  almost  universally  used  by 
scientists  today. 

The  origin  of  Ore  Shoots  is  not  fully  understood, 
although  we  know  they  exist,  and  their  characteristics  are 
also  well  known,  but  the  causes  are  not  fully  determined. 
However,  the  fact  that  they  always  occur  in  the  more  open 
and  porous  portions  of  veins  makes  it  obvious  that  such 
cavities  and  weak  spots,  due  to  earth  movements,  permit  the 
metalic  vapors  and  mineral  solutions  to  enter  and  deposit 
their  metallic  burden  to  form  ore  deposits.  It  is  a  universal 
natural  law  that  "all  forces  move  along  the  line  of  least 
resistance,"  and  the  forces  that  operate  in  the  formation  of 
ore  deposits  form  no  exception  to  the  general  rule. 


MINERAL  DEPOSITS 


207 


vig.  No.  55  shows  typical  Ore  Shoots,  illustrating  the 
ocurrence  of  ore  within  veins,  with  Ore  Shoots  and  "poor 
ground,"  alternating  along  the  course  of  the  ledge.  In  a 
system  of  veins  having  a  common  origin,  ore  is  found  oppos- 
ite ore,  and  barren  matter  opposite  barren  matter.  In  many 
mining  districts  mine  shafts,  or  shoots  in  parallel  veins,  form 
a  line  at  right  angles  to  the  strike  of  the  vein  system,  so  that 


Fig.  55.     Cross  Section  of  Vein  Showing  Occurance  of  Ore  Shoots. 

one   unfamiliar  with  the  district  often  concludes  the  veins 
run  contrary  to  the  real  course. 

In  a  vertical  section  of  a  vein  the  Shoots  likewise  are 
arranged  ore  opposite  ore.  (See  Fig.  56.) 

The  largest  and  richest  ore  shoots  are  usually  found  near 
the  middle  of  the  vein  system,  but  other  shoots  often  occur 
at  regular  intervals  along  the  course  of  the  vein,  sometimes 


208    PRACTICAL  GEOLOGY  AND  MINERALOGY 


with  25  to  50  feet  barren  ground  between,   and  at  other 
times  500  to  1000  feet  between  shoots. 

Fig.  No.  57  shows  one  vein  wall  removed,  the  shaded 
portions  representing  pay  ore  and  the  light  portions  the  poor 
ground.  These  shoots  are  ideal,  and  such  perfectly  defined 
sections  are  unusual.  It  must  not  be  inferred  that  the  ore 
differs  in  form  or  structure  from  the  barren  ground,  except 
that  the  ore  is  more  fractured  and  contains  all  the  values. 


Fig.  56.     Horizontal  Section  Showing  Ore  Shoots  in  Parallel  Veins. 

Shoots  go  from  the  surface  downward  to  various  depths. 
As  a  rule  they  are  deeper  than  they  are  long.  When  a 
Shoot  stops  at  a  shallow  depth,  it  is  called  a  Pocket.  Some 
ore  bodies  are  a  succession  of  pockets,  connected  by  only  a 
narrow  strip  of  ore,  or  at  times  by  only  a  "mud  seam." 

Ore  shoots  are  not  always  vertical,  but  may  pitch  to  the 
right  or  to  the  left.  They  are,  however,  generally  uniform 
in  any  vein  or  mineral  belt  in  their  general  characteristics. 


MINERAL  DEPOSITS 


209 


Veins  have  been  found  that  contain  ore  their  full  length,  and 
the  "shoot"  only  stops  because  the  vein  "pinches  out,"  but 
this  is  unusual. 

It  is  a  common  error  to  suppose  that  a  mining  claim  on 
the  same  vein  as  a  noted  ore  producer  will  become  equally 
valuable,  but  those  familiar  with  the  occurrence  of  ore  shoots 
never  commit  such  a  blunder.  Many  a  valuable  prospect 
has  been  abandoned  because  a  shaft  in  its  downward  course 
passed  out  of  an  ore  shoot  into  barren  ground.  Since  ore 

Fig.  57 


-ORE  CHUTES  AT  GOLD  COIN,  VICTOR,  COLORADO. 
bodies  vary  so  much,  it  "becomes  necessary  for  the  mining 
man  to  make  a  close  study  of  his  vein  to  avoid  mistakes  and 
useless  expense  in  mining  operations. 

Do  Veins  Grow  Richer  With  Depth? 

47.     In  the  early  history  of  lode  mining  in  California, 
it   was  thought  that  veins  decreased  in  value  with   depth. 


210    PRACTICAL  GEOLOGY  AND  MINERALOGY 


This  belief  was  due  largely  to  the  fact  that  "free  -gold" 
values  became  less  with  depth.  Many  good  mines  were 
abandoned,  until  science  devised  methods  of  extracting  the 


SURFACE. 


- ft.  level 


$.283-ft.lere/ 

fAST 


Ore  Ledge  matter  Oacite  Latite 

Fig.  58.     Section  of  a  Goldfield,  Nevada,  Mine. 

values  from  base  ores.  In  recent  years  a  popular  idea  has 
prevailed  amongst  fairly  well  informed  mining  men  that 
mines  grow  richer  with  depth;  this  may  or  may  not  be  the 
case,  owing  to  the  mining  district.  The  experience  in  a 


MINERAL  DEPOSITS  211 

developed  mine  is  usually  the  only  safe  guide  for  other  mines 
in  the  same  mineral  belt.  Those  who  believe  that  all  veins 
are  filled  and  mineralized  by  eruptive  metallic  matter  from 
the  earth's  interior  conclude  that  as  you  approach  "nature's 
Melting  Pot"  the  quantity  of  metal  should  increase.  Other? 
who  think  fissures  are  filled  from  above,  by  washing  into 
them  solid  metallic  elements,  reason  that  a  vein  must  grow 
richer  with  depth  because  "the  heaviest  always  goes  to  the 
bottom."  The  accepted  modern  theories  of  the  "Origin  of 
Ore  Deposits"  heretofore  named  compel  us  to  discard  these 
erroneous  notions. 

Deep  mining  operations  in  various  parts  of  the  world 
have  demonstrated  that  rich  ore  bodies  often  occur  at  the 
junction  of  different  rock  strata  (see  Fig.  62),  and  it  is 
equally  well  proven  that  rich  ore  bodies  are  often  found  at 
or  near  the  permanent  water  level.  It  is  the  rule  in  mining 
to  find  between  the  surface  and  the  water  level  a  section  or 
"Zone  of  Impoverishment"  (lean  ores)  followed  by  a  deeper 
zone  of  "high  grade"  at  the  water  level,  the  latter  being 
known  as  "Secondary  Enrichment,"  due  to  the  leaching  of 
the  ore  above  and  the  precipitation  of  the  metallic  contents 
below.  Sometimes  this  zone  of  "high  grade"  is  exclusively 
of  oxides  above  and  sulphides  below  the  water  level,  while  as 
mine  workings  reach  the  old  primary  ore  deposits  the  values 
grow  less  and  often  disappear  entirely. 

However,  this  rule,  like  all  others,  is  subject  to  excep- 
tions. Fig.  No.  58  represents  a  section  of  a  mine  at  Gold- 
field,  Nevada.  It  will  be  noticed  that  at  the  "Original  Water 
Level,"  the  shaded  portion  of  the  ledge  matter  representing 
ore,  tapers  out  to  a  point  and  "quits"  at  the  160  foot  level, 
only  to  reappear  below  the  old  water  level.  This  singular 
occurrence  is  common  in  the  principal  mines  of  that  particu- 


212     PRACTICAL  GEOLOGY  AND  MINERALOGY 

lar  mining  district.  It  will  also  be  noticed  that  the  vein 
and  ore  is  almost  vertical  above  water  level,  and  below  this 
the  dip  is  from  the  vertical  towards  the  east,  which  is  also 
contrary  to  the  general  rules  pertaining  to  dip  in  veins. 
The  ore  deposits  in  the  entire  Goldfield  district  are  abnor- 
mal, and  have  proven  a  puzzle  to  the  geologist  and  mining 
engineer. 

Facts  are  always  better  than  theories,  and  to  determine 
whether  mines  generally  grow  richer  with  depth  several 
eminent  authorities  have  compiled  statistics  of  the  principal 
mines  of  the  world,  which  show  that  in  the  majority  of  cases 
mines  do  not  increase  in  richness  with  depth,  but  on  the 
contrary  decrease  in  value,  if  not  in  the  size  of  the  vein  itself, 
at  from  1000  to  2000  feet  depth,  although  there  are  some 
remarkable  exceptions  to  this  rule.  Usually  the  most  profit- 
able period  in  a  mine  is  the  first  1000  feet  depth;  below  this, 
if  values  do  not  decrease,  the  extra  cost  of  hoisting  ore,  mine 
drainage  and  treating  the  more  refractory  ores  nearly  always 
makes  the  net  returns  less.  A  notable  exception  to  this  rule 
is  in  copper  veins,  many  of  which  are  unprofitable  until  the 
sulphides  are  reached. 

HOW  VEINS  ARE  CLASSIFIED 


Fissure  Veins — What  Are  They? 

48.  A  Fissure  is  a  crack  in  the  earth's  crust,  caused  by 
contraction  due  to  cooling,  which  is  enlarged  by  the  eruptive 
forces  within  the  earth.  A  Fissure  Vein  is  a  fissure  filled  by 
mineralized  matter.  Fig.  59  shows  an  ideal  .section  of  a 
Fissure  Vein.  At  the  left  is  seen  a  porphyry  dike  which 
frequently  accompanies  a  mineralized  Fissure  Vein,  and  such 
an  occurrence  is  always  welcome.  Adjoining  the  porphyry 


MINERAL  DEPOSITS 


213 


on  one  side,  and  also  next  the  gneiss  foot-wall,  is  seen  the 
Gouge  or  selvage,  which  is  usually  a  form  of  clay  or  talc 
resulting  from  decomposition  of  feldspar.  Sometimes 
"gouge"  occurs  in  the  middle  of  a  vein,  when  it  has  been 
reopened  by  earth  movements.  Often  this  gouge  matter 
contains  metallic  minerals,  and  is  characteristic  of  True 
Fissure  Veins,  usually  serving  as  a  guide  in  following  a 
vein  that  is  somewhat  broken  up;  when  a  vein  is  narrowed 
down  to  a  thin  seam,  the  gouge  matter  is  continuous. 

Fig.  59 


—IDEAL,  SECTION  OF  A  FISSURE  VEIN. 

The  "Mill  dirt  and  quartz"  constitute  the  Gangue, 
usually  forming  "low  grade  ore."  The  "Pay-Streak"  is  the 
"high-grade"  ore.  As  the  gangue  must  usually  be  removed 
along  with  the  Pay-Streak,  the  value  of  the  ore  in  such  a 
vein  is  represented  by  an  average  taken  across  from  wall  to 
wall. 

A  True  Fissure  Vein  has  polished  walls,  which  are  more 
or  less  "striated"  (scratched)  by  friction,  to  which  they  are 
subjected  by  earth  movements  after  the  vein  was  formed, 
these  smooth  wall  surfaces  being  known  as  "Slickensides." 


214     PRACTICAL  GEOLOGY  AND  MINERALOGY 

A  fissure  vein  has  both  hanging  and  foot  walls  of  the 
same  kind  of  rock,  although  in  passing  through  sedimentary 
strata  the  divided  rock  strata  may  be  somewhat  Faulted. 
Fissure  veins  in  crystaline  rocks,  like  granite,  have  both 
walls  granite,  although  the  character  of  the  granite  may  be 
somewhat  different.  A  fissure  vein  may  in  some  part  of  its 
course  follow  the  dip  of  the  stratified  rock,  and  may  thus  be 
mistaken  for  a  Bed,  but  if  with  depth  the  vein  cuts  across  a 
strata  it  may  be  pronounced  True  Fissure  Vein. 

The  normal  position  of  a  Fissure  Vein  is  an  upright  one, 
but  a  slipping  of  the  hanging  wall  rocks  may  throw  the  vein 
into  a  horizontal  position  and  produce  what  is  called  a 
Blanket  Fissure  Vein,  which  is  sometimes  mistaken  for  a 
"bedded  deposit." 


Fig.  60 


b     a 


.— Section,  of  a  Fissure  Vein,  showing  banded  structure, 
o  a,  country  rock }  b  b,  calc  spar ;  c  c,  galena ;  d  d,  heavy  spar— sulphate  of 
baryta ;  e  e.  comb.v  ouartz. 

Fissure  Veins  often  have  a  "Banded"  or  "Ribbon"  struc- 
ture as  shown  in  Fig.  60.  In  this  type  of  veins,  which  is  not 
uncommon,  the  ore  is  arranged  in  alternate  bands  or  layers 
in  accordance  with  the  successive  growth  of  the  vein  filling. 
In  the  Figure,  b,  b — is  calc  spar,  which  may  carry  lead  ore ; 
c,  c — may  carry  manganese;  d,  d — copper,  while  the  center 
bands  e,  e,  may  consist  of  a  mixture  of  all  the  ores  named. 
Sometimes  seams  of  talc  or  gouge  occur  between  the  differ- 


MINERAL  DEPOSITS  215 

ent  bands  as  well  as  in  the  center  streak.  This  banded 
structure  is  peculiar  to  Fissure  Veins,  but  all  Fissure  Veins 
are  not  banded. 

The  Theory  of  Origin  of  Banded  Veins  is  somewhat  as 
follows : 

First  there  is  a  crack,  or  fault,  in  the  rocks,  which  opened 
to  receive  metalic  solutions  which  formed  the  center  bands 
ef  e.  Earth  movements  cause  a  reopening  of  the  fissure,  and 
the  solutions  enter  along  the  walls  to  form  bands  d,  d; 
refissuring  causes  the  walls  to  further  spread  and  new  solu- 
tions enter  to  form  e,  e;  a  repetition  of  the  process  results 
in  the  bands  b,  b,  leaving  the  walls  d,  d,  at  the  close  of  the 
epochs  widely  separated,  which  in  the  original  fault  were 
contiguous. 

In  the  early  history  of  mining  ore  bodies  were  supposed 
to  be  confined  to  fissure  veins  in  granitic  rocks  of  the  Arch- 
ian  age,  and  while  fissure  veins  are  of  greater  length  and 
more  continuous  in  depth,  yet  later  mining  experience  has 
shown  other  forms  of  veins  to  be  equally  important  sources 
of  ore  bodies. 

Fig.  61  shows  an  ideal  section,  illustrating  fissure  veins 
and  their  general  characteristics.  At  A  is  seen  a  fissure 
vein  in  Rhyolite,  both  walls  the  same  igneous  rock.  B  and  C 
are  True  Fissure  Veins  proceeding  out  of  granite,  a  crystal- 
line rock,  and  cutting  strata  of  slate,  limestone  and 
sandstone,  all  sedimentary  rocks.  At  D  is  seen  a  somewhat 
different  type  of  vein,  the  Rhyolite,  an  igneous  rock  forms 
one  wall,  the  other  wall  being  formed  by  both  sedimentary 
and  crystalline  rocks  forming  what  is  called  a  Contact 
Fissure. 


216    PRACTICAL  GEOLOGY  AND  MINERALOGY 

How  May  the  Age  of  Fissure  Veins  Be  Determined? 

49.  There  are  several  kinds  of  Fissure  Veins  as  well  as 
fissures  of  various  age,  some  are  barren  and  others  valuable, 
so  it  becomes  every  mining  man  to  be  able  to  tell  the  relative 
age  and  importance  of  veins  when  they  are  found  to  intersect 
one  another. 

As  a  general  rule  it  may  be  said  that  the  older  veins  are 
the  best  mineralized,  and  the  younger  veins  of  least  import- 


Fig.  5 1 .     Ideal  Geological  Section,  Illustrating  Fissure  Veins. 

ance.  The  older  fissures  usually  follow  the  trend  of  the  hills 
or  mountains  while  cross  fissures  are  usually  younger  and  of 
less  importance  as  a  source  of  metals.  When  one  fissure 
meets  another  at  something  like  a  right  angle,  the  older  vein 
is  always  faulted  by  the  younger.  Fissures  having  the  same 
dip  usually  have  the  same  origin  and  age,  while  as  a  rule 
those  having  opposite  dip  belong  to  different  periods. 


MINERAL  DEPOSITS  217 

Contact   Veins — What   Are   They? 

50.  A  Contact  in  mining  means  the  meeting  of  two  dif- 
ferent formations,  and  a  Contact  Vein  is  the  filled  cavity  that 
occurs  along  the  plane  of  contact  of  dissimilar  rocks.  Contact 
Veins  usually  occur  at  the  junction  of  eruptive,  or  crystalline 
rocks,  with  sedimentary  or  stratified  rocks,  but  they  are  some- 
times found  between  unlike  stratified  rocks,  as  at  the  junction 
of  shale  and  sandstone  with  limestone,  in  which  case  they  are 
likely  to  be  mistaken  for  bedded  deposits. 

Contact  Veins  are   formed  by  the  intrusion  of  igneous 
rocks  into  sedimentary  rock  strata.     Fig.  No  62  shows  con- 
Fig.  62 


ILLUSTRATING  CONTACT  VEINS. 

tact  veins  occurring  between  limestone  and  porphyry,  the 
latter  having  been  forced  up  through  a  fissure,  and  while 
in  a  plastic  state  spread  out  sheet-like  at  the  surface,  between 
which  and  the  limestone  beneath  a  Blanket  Contact  Vein 
was  formed.  The  soft  porous  limestone  disintegrates  rapidly 
forming  cavities  in  which  the  metallic  solutions  deposit  their 
solid  matter  to  form  ore. 

The  uplifting  of  mountains  through  giant  fissures  in 
sedimentary  rocks  forms  contacts  of  great  extent.  The 
sedimentary  rocks  adjacent  are  usually  tipped  up,  and  a  series 


218    PRACTICAL  GEOLOGY  AND  MINERALOGY 

of  contact  veins  may  result  as  shown  in  Fig.  63.  Here  the 
diorite  mountain  at  the  left  was  apparently  intruded  after 
the  sedimentary  rocks  had  been  formed.  The  main  contact 
shown  at  the  left  is  between  slate  and  diorite  at  the  surface, 
and  with  depth  the  slate  disappears,  leaving  a  contact  be- 
tween limestone  and  diorite,  along  which  was  formed  the 
principal  ore  deposit  of  the  district.  The  other  contact  veins 
shown  in  the  Figure  partake  of  the  nature  of  beds  which 
have  subsequently  become  mineralized. 

Fig.  63 


—ORE  DEPOSITS.  MINNIE  MOORE  MINE,  IDAHO. 

Contact  veins  occur  in  California  between  granite  .and 
slate  in  a  somewhat  vertical  position.  In  Colorado  the  ores 
of  the  Leadville  District  occur  in  "Blanket  Contacts,"  of 
limestone  and  dolomite  with  quartzite  and  porphyry. 

Contact  veins  are  next  in  importance,  as  ore  bearers,  to 
fissure  veins,  and  some  regard  them  with  greater  favor  than 
all  other  veins,  although  not  so  extensive  in  strike  and  depth 
as  fissure  veins. 

A  Contact  Fissure  Vein  partakes  of  the  nature  of  both 
contact  and  fissure  veins.  The  walls  are  dissimilar,  but  one 
wall  conforms  with  the  foliation  of  the  stratified  rocks  while 


MINERAL  DEPOSITS 


219 


the  other  wall  may  be  a  crystalline  rock,  or  composed  of 
stratified  rocks  in  the  upper  course  with  a  faulted  igneous 
rock  below. 

Fig.  No.  64  is  an  ideal  section,  illustrating  Contact  Veins. 
At  B — is  a  contact  between  Gneiss  and  Slate;  C — is  a  con- 
tact between  Slate  and  Limestone.  At  D — is  shown  a 
contact  having  both  walls  sedimentary  rocks;  at  G — is  seen 
a  Blind  Fissure  Vein,  and  E — is  a  True  Fissure  Vein,  both  of 
which  have  been  faulted. 


Fig.  64.     Ideal  Section  Illustrating  Contact  Veins. 

Gash  Veins — What  Are  They? 

51.  Gash  Veins,  as  the  name  indicates,  are  simply  filled 
gashes  or  surface  fissures.  They  usually  taper  to  a  point  in 
their  downward  course  and  disappear.  As  a  rule  they  are  a 
most  unsatisfactory  type  of  veins,  and  when  mineralized  little 
dependence  can  be  placed  on  them,  although  they  often  con- 
tain pay  ores.  Many  lead  deposits  in  the  Mississippi  Valley 
occur  in  typical  Gash  Veins,  largely  in  limestone  rocks,  the 


220     PRACTICAL  GEOLOGY  AND  MINERALOGY 

ore  forming  in  bunches,  at  the  intersection  of  different  rock 
strata,  where  the  metallic  particles  are  concentrated,  either 
from  leached  wall  rocks  or  from  circulating  waters  in  fissures 
adjacent  to  such  Gash  Veins.  An  occasional  Gash  Vein  is 
found  in  volcanic  rocks  as  seen  at  B  in  Fig.  65.  At  C  is 
seen  a  Contact  Gash  Vein  between  volcanic  and  sedimentary 
rocks;  D  and  E  are  typical  Gash  Veins  in  stratified  rocks, 
the  True  Fissure  Vein  at  F  shown  by  contrast,  cutting  across 
the  stratification  and  continuing  downward  in  undiminished 
size. 


Fig.  65.     Ideal  Section  Illustrating  Gash  Veins. 

What  Are  Segregation  Veins? 

52.  Segregation  Veins  conform  to  the  foliation  of  the 
enclosing  rocks,  and  the  ore  in  such  veins  is  usually  arranged 
in  lenses,  or  in  the  form  of  kidneys.  They  differ  from  con- 
tact and  bedded  veins  in  the  irregularity  of  ore  in  structure 
of  vein  and  in  arrangement  of  the  minerals  within  the  vein. 
Segregation  veins  often  have  a  banded  structure  like  fissure 
veins,  but  differ  from  them  in  showing  no  evidence  of  fault- 


MINERAL  DEPOSITS  221 

ing,  and  in  always  following  the  folding  and  twisting  of  the 
wall  rocks.  Fig.  66  shows  the  most  common  occurrence  of 
ore  in  segregation  veins  in  crystalline  and  other  rocks.  The 
lead-silver  mines  in  Idaho  occur  in  rocks  of  slate  and  quartz- 
ite,  the  ore  forms  in  pockets  or  large  masses.  Many  low 


Fig.  66.     Ideal  Section,  Illustrating  Segregation  Deposits. 

grade  mines  in  the  Black  Hills  of  South  Dakota,  occurring 
in  schist,  belong  to  this  class.  Segregation  veins  are  not 
uncommon  elsewhere,  and  are  as  well  defined  as  Simple 
Fissure  Veins,  but  more  irregular  in  ore  arrangement. 


222     PRACTICAL  GEOLOGY  AND  MINERALOGY 


IREGULAR  ORE  DEPOSITS 


53.  Irregular  Deposits,   as  the  name  indicates,  are  of 
more  complex  origin  and  less  uniform  in  occurrence.     Such 
deposits  have  no  regularly  defined  walls,   nor  fixed   limits, 
hence  it  is  difficult  to  estimate  their  extent  or  permanence. 
These  are  classed  under  three  heads,  as  follows: 

(1)  Chamber  Deposits. 

(2)  Impregnation  and  Stockwork. 

(3)  Fahlbands. 

What  Are  Chamber  Deposits? 

54.  Chamber  Deposits  are  cavities  filled  with  ore,  some- 
times called   "Cave  Deposits,"   for  the  reason  that  it  was 
believed  caves  were  first  formed  and  afterwards  filled  with 
ore.     The    origin  of  such  deposits  is  not  thoroughly  under- 
stood, hence  open  to  controversy.    From  the  fact  that  Cham- 
ber  Deposits   usually  occur   in   limestone   or   other   soluble 
rocks,  it  is  believed  that  cavities  were  first  formed  by  the 
dissolving  action  of  surface  waters,  and  the  metallic  minerals 
were  later  deposited  in  such  cavities  from  mineral  solutions, 
circulating    through    fissures    in    the   country    rocks.      Some 
authorities  contend  that  the  metallic  substances  in  chamber 
deposits  are  derived  from  the  country  rocks  by  replacement 
(see  Par.  19)  ;  that  is,  the  mineral  solutions  after  depositing 
their  metallic  content,  took  up  an  equal  amount  of  soluble 
rock  matter  and  deposited  it  at  lower  levels.    This  process  of 
substitution,  it  is  assumed,  was  continued  through  the  ages, 
and  resulted  in  the  chamber  deposits  found  throughout  the 
world  today.    The  weight  of  authority,  however,  inclines  to 
the  opinion  that  the  ore  in  chambers  wTas  derived  in  a  manner 
similar  to  that  found  in  fissure  veins,  due  to  complex  fissuring 


\  MINERAL  DEPOSITS 223 

and  faulting,  forming  open  conduits  connecting  with  cavities 
in  which  the  ore  now  occurs. 

Fig.  No.  67  shows  a  series  of  Ore  Chambers  in  limestone 
and  igneous  rocks. 

The  presence  of  igneous  dikes  adjacent  to  ore  chambers 
seems  to  confirm  the  view  that  the  ore  is  derived  from  below, 
as  in  regular  vein  formation. 

It  is  an  admitted  fact  that  chamber  deposits  are  seldom 
found  below  the  natural  water  level,  which  makes  the  future 


Fig.  67.  Ideal  Section  Illustrating  Chamber  Deposits. 

of  such  mines  uncertain,  while  adjoining  mines  gain  no 
prestige  by  virtue  of  their  association,  as  in  a  regular  vein 
formation.  Several  lead  mines  of  the  Mississippi  Valley  and 
most  lead-silver  mines  of  the  Rocky  Mountain  and  Pacific 
Coast  regions  belong  to  this  class.  The  Jerome,  Arizona, 
copper  Chamber  Deposits  occur  in  Azoic  rocks,  as  shown  in 
A,  Fig.  67,  while  the  Bisbee  District  (Arizona)  copper 
Chamber  Deposits  occur  in  limestone  rocks ;  but  whatever  the 
formation  such  deposits  are  always  associated  with  quartz 


224     PRACTICAL  GEOLOGY  AND  MINERALOGY 

and  porphyry.  Chamber  Deposits  of  gold  and  silver  are  rare, 
although  these  metals  are  frequently  found  associated  in 
small  quantities  with  copper  and  lead  Chamber  Deposits. 

What  Are  Impregnation  and  Stockwork  Deposits? 

55.  Impregnation  and  Stockwork  are  so  similar  in  origin 
and  occurrence  that  they  may  properly  be  classed  under  the 
same  head,  although  several  authors  treat  them  as  distinct 
types  of  deposits. 


:  v 


Fig.  68.  Ideal  Section  Illustrating  Segregation  and  Stockwork  Deposits. 

Impregnations  are  so  closely  allied  to  fissures  that  they 
are  sometimes  called  Impregnation  veins.  They  usually  occur 
with  narrow  fissures  in  the  more  open  and  porous  rocks,  the 
more  soluble  elements  like  lime,  feldspar,  etc.,  are  dissolved 
out,  and  the  cavities  left  are  filled  by  replacement  or  by  a 
substitution  of  metallic  elements  from  solutions  for  these 
dissolved  out  of  the  wall  rocks.  Where  the  vein  material  is 
very  hard  the  wall  rocks  may  become  more  highly  mineralized 
than  the  vein  itself.  Fig.  68  illustrates  Stockwork  and  Im- 
pregnation Deposits.  At  B  is  shown  an  Impregnation  Ore 
Deposit,  being  a  fissure  with  an  arrangement  of  ore  in  the 


MINERAL  DEPOSITS  225 

vein  as  well  as  in  enclosing  rocks.  The  Ore  Deposits  in  the 
Goldfield,  Nevada,  district,  partake  ofthe  nature  of  impreg- 
nations, the  veins  occurring  in  volcanic  rocks  like  andesite, 
rhyolite,  etc.,  while  the  vein  filling  is  a  hard  jaspar  quartz. 
Where  earth  movements  have  broken  up  the  vein  matter,  ore 
shoots  are  confined  entirely  to  the  vein  matter,  but  often  the 
wall  rocks  are  more  highly  mineralized  than  the  vein  itself, 
and  the  only  way  to  tell  ore  from  "waste"  is  by  the  presence 
or  absence  of  metal  values.  At  A,  in  Fig.  68,  is  shown  a 
Stockwork  similar  to  Impregnation,  except  that  the  minerali- 
zation extends  farther  out  into  the  wall  rocks  and  little  vein- 
lets  are  seen  running  here  and  there,  characteristic  of  Stock- 
work.  At  C  is  seen  Stockwork,  unconnected  with  a  vein, 
being  simply  a  section  of  country  rock  filled  with  veinlets  of 
ore,  making  the  origin  very  uncertain,  but  the  presence  of 
dikes  adjacent  to  such  Stockwork  indicates  the  mineralization 
took  place  through  the  medium  of  the  dikes. 

Such  deposits  occur  in  different  geological  formations, 
usually  in  the  more  brittle  primitive  rocks,  but  they  never 
continue  below  the  oxide  zone,  while  many  do  not  extend 
more  than  100  feet  below  the  surface. 

The  origin  of  Stockwork  is  believed  to  be  due  to  a  sudden 
cooling  of  the  hot  crystalline  rocks,  by  the  inrushing  of  surface 
waters,  causing  fractures  and  cavities  into  which  mineral 
solutions  entered  to  deposit  their  metallic  burden. 

Impregnation  and  Stockwork  Deposits  occur  in  many 
parts  of  the  world,  producing  many  ore  deposits  valuable 
enough  to  be  profitably  worked.  In  Idaho  such  deposits  of 
gold,  silver  and  lead  occur  in  schist  and  quartzite.  Many  low 
grade  mines  in  Colorado  and  the  tin  deposits  of  England  and 
Germany  occur  in  Impregnations  and  Stockworks. 


226    PRACTICAL  GEOLOGY  AND  MINERALOGY 


What  Are  Fahlbands? 

56.  Fahlband  Deposits  are  accumulations  of  metallifer- 
ous minerals  in  certain  soft  and  porous  rock  strata,  usually 
schists  and  shales.  Fissures,  cutting  through  rock,  are  found 
to  bear  ore  when  they  intersect  porous  rock  strata,  or  Fahl- 


Fig.  70.     Ideal  Section  Illustrating  Fahlband  Deposits. 

bands,  and  in  passing  into  a  hard  strata  of  crystalline  rock 
become  practically  barren.  This  alternate  arrangement  of 
hard  and  soft  rock  strata  is  favorable  to  the  production  of 
Fahlband  Deposits,  which  not  only  include  the  mineralized 
portion  of  the  vein,  but  also  the  fahlband  rocks  cut  by  the 
fissures. 

Fig.  69  shows  a  horizontal  section  of  Fahlband  Deposits. 
The  shaded  strata  are  the  Fahlbands  and  the  lighter  colored 
strata  represent  the  crystalline  rocks.  A,  B  and  C  are  Fis- 
sures, cutting  across  the  formations;  D  and  E  are  ore  bodies 
formed  within  the  fahlbands,  while  the  entire  fahlbands  are 
often  mineralized  so  as  to  form  low  grade  ores. 

The  origin  of  Fahlband  Deposits  is  a  matter  of  dispute. 
Some  contend  that  the  metallic  substances  are  derived  from 


MINERAL  DEPOSITS  227 

the  country  rocks  by  "replacement"  according  to  that  theory 
(See  Par.  21).  But  the  fact  that  Fahlband  Deposits  occur 
adjacent  to  fissure  veins  makes  it  appear  more  reasonable  that 
their  origin  is  due  to  the  metallic  solutions  entering  the 
porous  rocks  from  the  fissures,  hence  they  do  not  differ  mater- 
ially in  origin  from  the  other  classes  of  deposits  previously 
described. 

Fahlband  Deposits  occur  in  the  Jura-Trias  shales  of 
California.  The  immense  low  grade  ore  bodies  of  South 
Dakota,  averaging  $3.50  to  $4.00  per  ton,  are  mainly  Fahl- 
band Deposits  in  schists.  Ore  bodies  occurring  in  Fahlbands 
are  usually  lens-shaped  and  several  hundred  feet  across.  In 
Norway  a  Fahlband  zone  is  known  to  be  100  miles  long  and 
50  miles  wide,  being  worked  for  the  ores  contained  in  narrow 
fissure  veins. 

What  Are  the  Common  Errors  in  Regard  to  Ore 
Deposits? 

57.  Many  mistaken  notions  prevail  in  regard  to  mining 
in  general  and  ore  deposits  in  particular,  and  it  will  no  doubt 
prove  of  interest,  if  not  profit,  to  refer  to  some  of  these.  They 
may  be  grouped  into  two  classes : 

(1)  Mistakes  due  to  ignorance- and  inexperience,  and 

(2)  Mistakes  due  to  experience  with  bad  judgment. 

(1)   MISTAKES  DUE  TO  IGNORANCE  AND  INEXPERIENCE 

58.  Mistakes  due  to  these  causes  are  natural  and  to  be 
expected,  but  they  may  be  prevented  by  mining  knowledge 
and  practical  mining  experience,  so  it  may  not  be  amiss  to 
notice  the  most  prominent. 

Many  hard  headed  business  men,  who  have  succeeded  in 
commercial  lines,  assume  that  they  can  be  equally  successful 


228     PRACTICAL  GEOLOGY  AND  MINERALOGY 

in  mining  without  any  knowledge  whatever  of  the  science  of 
mining.  Others  regard  mining  as  a  mere  matter  of  "Chance," 
but  the  mission  of  this  book  will  have  failed  if  any  reader  falls 
into  such  fatal  errors. 

Fig.  73 


COMPOSITE    VEIN     CROESUS    MfNE.    IDAHO. 

An  equally  grievous  error  of  the  unlearned  and  inexperi- 
enced is  to  disregard  all  geological  formations  and  adopt  the 
slogan  that  "Gold  is  where  you  find  it,"  and  to  assume  that 
you  are  as  apt  to  find  a  gold  mine  in  digging  a  well  or  driving 
a  water  tunnel  as  anywhere  else. 


MINERAL  DEPOSITS  229 

A  common  saying  amongst  the  unlearned  and  inexperi- 
enced is  that  "One  man  can  see  as  far  into  the  ground  as 
another;"  in  other  words,  that  the  novice  in  mining  knows 
as  much  of  what  is  below  as  the  mining  engineer.  So  far  as 
the  physical  eye  is  concerned  one  man's  sight  may  be  as  good 
as  another's,  but  the  scientific  eye  can  penetrate  solid  rocks 
and  often  see  more  than  the  untrained  eye  can  see  after  a 
shaft  is  sunk. 

Many  who  are  ignorant  of  vein  formation  and  the  princi- 
ples underlying  ore  deposits,  jump  at  the  conclusion  that  a 
mining  claim  adjoining  a  rich  mine  will  prove  equally  valu- 
able. Such  a  thing  does  now  and  then  happen,  but  it  will  not 
do  to  act  on  such  a  supposition. 

(2)   MISTAKES  DUE  TO  EXPERIENCE  WITH  BAD  JUDGMENT 

59.  It  must  not  be  thought  that  experience  will  always 
guard  against  errors.  Experience  is  a  good  teacher,  but  many 
fail  to  learn  with  the  best  of  teachers,  and  go  on  making  the 
same  mistakes  over  and  over  again.  However  wisdom  and 
experience  amalgamated  make  a  safe  guide  and  will  prevent 
the  errors  which  are  all  too  common  in  mining  operations. 

A  common  error  is  for  a  miner  to  judge  every  mining 
section  by  his  experience  in  a  particular  district,  and  it 
frequently  happens  that  a  prospector  removing  to  a  new 
country  utterly  fails  because  he  expects  to  find  rock  formation 
and  ore  deposits  like  those  at  the  old  "strike."  Old  Comstock 
miners  removing  to  new  districts  were  wont  to  believe  that  no 
ore  deposits  of  value  could  occur  unless  accompanied  by 
porphyry-dikes,  but  many  learned  their  error  when  it  was  too 
late.  Many  California  miners  in  the  "Contact"  district  today 
believe  that  no  gold  veins  can  be  profitable  unless  they  have 
a  slate  hanging  wall  and  a  granite  foot-wall,  because  of  their 


230    PRACTICAL  GEOLOGY  AND  MINERALOGY 

experience  in  that  particular  district,  but  as  a  matter  of  fact 
such  a  combination  is  rare  in  the  world's  best  mines. 

Likewise  Granite  was  once  considered  unfavorable  for 
precious  metal  ores,  because  veins  in  the  Mother  Lode  region, 
occurring  in  granite,  had  proved  unprofitable,  but  veins  in 
granite  in  other  portions  of  California,  in  Nevada,  Idaho  and 
Utah,  have  proven  this  idea  to  be  wholly  false. 

In  early  days,  Limestone  was  "passed  up"  by  miners,  but 
Leadville,  Colorado,  and  Eureka,  Nevada,  deposits  of  silver- 
lead  have  proven  that  limestones  may  not  be  wholly  dis- 
regarded in  mining  operations. 

As  a  rule  sedimentary  rocks  are  unfavorable  for  ore 
deposits,  but  the  Silver  Reef  Mines  of  Utah,  occurring  in 
sandstone,  have  proven  a  notable  exception. 

Early  California  miners  believed  rich  gold  ores  existed 
only  near  the  surface,  and  frequently  abandoned  their  mines 
at  a  depth  of  a  few  hundred  feet,  but  it  remained  for  later 
generations  to  upset  this  prejudice  by  sinking  to  a  depth  of 
nearly  a  mile  in  several  mines  all  in  profitable  ore. 

Present  day  miners  often  make  the  mistake  of  going  to  the 
other  extreme  in  assuming  that  all  mines  grow  richer  and 
veins  larger  with  depth.  It  is  quite  generally  true  that  copper 
mines  do  increase  in  value  with  depth  and  few  miners  expect 
great  copper  values  until  the  sulphide  ores  are  reached,  but  it 
will  not  do  to  jump  at  the  conclusion  that  all  mines  grow 
richer  with  depth,  for,  as  it  has  been  previously  shown  (Par. 
47),  the  reverse  is  true  in  a  majority  of  the  world's  mines. 

From  these  observations,  we  should  understand  that  while 
the  character  of  rock  formation  is  a  good  "indicator,"  it  will 
not  do  to  jump  at  the  conclusion  that  ore  deposits  are  confined 
entirely  to  any  one  class  of  veins  or  rock  formation,  nor  that 


MINERAL  DEPOSITS  231 

rich  ores  are  confined  to  surface  workings,  nor  found  only  at 
great  depths.  The  practical  mining  man  should  be  conserva- 
tive. Form  opinions  he  must,  as  all  will  who  use  their  reason- 
ing powers,  but  definite  conclusions  and  fixed  opinions  should 
not  be  formed  except  on  strong  evidence  and  corroborative 
proofs.  He  should  rather  regard  the  old  maxim,  "Prove  all 
things  and  hold  fast  to  that  which  is  true." 

General  Principles  Governing  Ore  Deposits 

60.  From  what  has  previously  been  stated  it  must  be 
evident  that  no  hard  and  fast  set  of  rules  can  be  laid  down 
in  regard  to  ore  deposits. 

Certain  physical  and  chemical  agencies  appear  to  have 
been  more  active  in  certain  districts  than  in  others,  and  this 
has  produced  quite  a  variety  of  ore  deposits,  but  certain 
fundamental  principles  underly  them  all,  so  that  ore  deposits 
are  much  the  same  the  world  over. 

The  mining  industry  has  now  reached  such  a  stage  that 
every  important  mine  and  district  throughout  the  world  has 
been  observed  and  a  record  made  of  their  characteristics,  so  it 
is  now  possible  to  formulate  rules  based  upon  actual  experi- 
ence, and  these  may  be  stated  as  follows : 

(1)  VEIN  RULES. 

61.  (a)   Veins  that  follow  the  trend  of  mountain  ranges 
are  generally  well  defined  and  the  most  productive. 

(b)  Veins  which  cut" across  mountains  or  hills  are  gen- 
erally of  a  later  geologic  age  and  imperfectly  mineralized. 

(c)  When  a  vein  is  faulted  by  another  vein,  the  faulted 
vein  is  the  older,  and  usually  the  most  productive. 

(d)  Parallel  veins  of  certain  known  strike  and  dip  have 


232     PRACTICAL  GEOLOGY  AND  MINERALOGY 

the  same  origin  and  are  usually  better  mineralized  than  those 
that  vary  a  few  degrees  from  the  common  course. 

(e)  Veins  of  hard  material  are  usually  "lean"  and  some- 
times absolutely  barren,  while  the  softer  and  more  porous 
sections  of  all  veins  are  the  most  favorable  for  ore  deposits. 

(2)  COUNTRY  ROCK  RULES. 

62.  (a)   Crystalline  rocks  are  the  most  favorable  for  ore 
deposits,  but  contacts  of  igneous  with  sedimentary  rocks  are 
also  very  favorable  for  rich  ores. 

(b)  Intrusive  volcanic  rocks  that  tip  up  formations  nearly 
vertical  are  most  frequently  associated  with  well  mineralized 
veins. 

(c)  Porphyry  rocks  in  or  adjacent  to  veins  constitute  a 
favorable  indication  for  valuable  ore  deposits. 

(d)  Quartz-porphyries  are  generally  associated  with  ex- 
tensive copper  deposits. 

(e)  The  nearer   a  vein   approaches  a  vertical   position, 
especially  above  the  water  level,  the  richer  the  ore  is  likely 
to  be. 

(3)  ORE  SHOOT  RULES. 

63.  (a)   Ore  generally  arranges  itself  into  clusters  or 
bunches,  to  conform  with  the  dip  and  cleavage  of  the  enclos- 
ing walls. 

(b)  Ore  bodies  in  a  parallel  vein  system  generally  occur 
in  cross  zones,  ore  opposite  ore  and  barren  ground  opposite 
barren  ground. 

(c)  Ore  is  usually  richer  in  the  narrower  and  pinched 
portions  of  a  vein,  and  lower  grade  in  the  wider  portions. 


MINERAL  DEPOSITS 233 

(d)  High  grade  ore  usually  occurs  at  the  inrersection  of  a 
dike,  or  another  vein,  with  a  mineralized  vein. 

(e)  Enlarged  ore  bodies  generally  occur  in  a  fissure  vein 
where  it  passes  from  one  class  of  rock  into  another. 

(f)  Gold  ores  as  a  rule  are  more  profitable  in  the  oxide 
zone  and  frequently  decrease  in  ton  value  below  the  water 
level. 

(g)  Gold  ores  with  values  largely  in  pyrites  seldom  yield 
value  after  pyrites  change  to  marcasite,  or  white  iron. 

(h)  Ore  enrichment  usually  occurs  when  a  vein  changes 
in  strike  or  dip,  but  this  often  gives  way  to  lean  ore  below  the 
point  of  enrichment. 

(4)   MISCELLANEOUS  RULES. 

64.  (a)  A  heavy  iron  capping  (Hat  or  Gossan)  at  the 
vein  outcrop,  indicates  extensive  sulphide  ore  bodies  at  depth. 

(b)  Oxides  and  carbonates  of  copper  and  lead,  resulting 
from  the  decomposition  of  sulphides  of  those  minerals,  never 
continue  below  the  natural  water  level,  where  they  change  to 
sulphides. 

(c)  Local  enrichments  of  oxide  and  carbonate  minerals 
result  from  leaching  of  ore  above,  whose  metallic  elements 
are  precipitated  below. 

(d)  Deposits  of  Mercury  ore   (Cinnabar)   rarely  occur 
in  paying  quantities  except  in  porous  serpentine,  or  sandstone 
rocks,  which  have  been  faulted  by  intrusions  of  igneous  rocks. 

(e)  Intrusions  of  porphyry  or    quartz-porphyry    when 
occurring  in  or  near  a  vein  are  favorable  indications  of  valu- 
able ore  deposits. 


234     PRACTICAL  GEOLOGY  AND  MINERALOGY 

(5)   GENERAL  OBSERVATIONS. 

65.  All  rules,  whether  pertaining  to  mining  or  other- 
wise, have  their  exceptions.     Some  rules  that  fit  perfectly  to 
conditions  in  one  district  may  be  only  partially  applicable  to 
another  district,  so  if  certain  rules  given  are  found  in  perfect 
accord  with  a  mine   in  which  you  are  interested,  you  can 
safely  conclude  these  same  principles  control  all  the  deposits 
in  the  district  having  the  same  origin.    It  must  not  be  assumed 
however  that  because  one  mine  on  a  lode  proves  rich,  all  others 
will  be  equally  valuable,  but  if  a  mine  in  a  given  district,  in 
the  undeveloped  stage,  shows  the  same  characteristics  and  is 
equally  rich  on  the  surface  as  another  fully  developed  mine,  it 
may  be  reasonably  assumed  that  similar  results  will  follow  as 
in  the  developed  mine. 

How  Do  Faults  Affect  Ore  Bodies? 

66.  Faults  in  rock  masses  have  previously  been  explained, 
and  the  influence  of  faults  in  producing  the  conditions  favor- 
able to  the  formation  of  ore  bodies  has  also  been  considered 
(See  Par.  37),  but  the  forces  that  produce  faults  never  cease, 
so  that  after  a  perfect  ore  body  has  been  formed  by  nature's 
processes,  these  are  often  dislocated  by  subsequent  earth  move- 
ments, so  that  what  was  once  a  continuous  ore  body  is  often 
divided  up  into  sections  more  or  less  widely  separated  from 
each  other,  which  makes  it  also  necessary  to  consider  faulted 
ore  bodies. 

Many  a  promising  prospect  or  mine  has  been  abandoned 
because  the  ore  "quit."  Afterwards  some  miner  with  a  little 
scientific  knowledge  of  faulted  ore  bodies  has  taken  up  the 
abandoned  work  and  located  the  lost  ore  body,  perhaps  richer 
than  before. 

When  an  ore  body  splits  in  its  downward  course,  or  thins 


MINERAL  DEPOSITS  235 

out  to  a  point  and  finally  quits,  further  work  is  usually  fruit- 
less, but  where  a  vein  of  ore  is  cut  off  abruptly,  work  should 
not  be  discontinued,  as  the  ore  has  simply  been  dislocated  by 
faulting,  and  a  little  practical  knowledge  will  usually  enable 
the  miner  to  find  the  continuation  of  the  ore  body.  A  fault 
should  never  condemn  a  mine  or  prospect,  as  faulted  ore 
bodies  frequently  occur  in  the  world's  greatest  mines,  in  fact 
a  perfectly  continuous  ore  body  is  rather  rare. 

A  vein  may  be  faulted  by  another  vein,  the  two  continuing 
as  one  for  a  time,  and  then  each  may  resume  its  original  strike 
and  dip.  In  such  a  case,  there  is  no  difficulty,  as  the  ore  is 
continuous,  and  often  of  increased  value  as  a  result  of  the 
fault.  A  vein  is  often  faulted  by  a  dike,  and  in  that  case 
only  a  section  of  the  ore  body,  the  width  of  the  dike,  is  dis- 
located by  the  intrusion,  and  the  continuation  of  such  a  faulted 
vein  or  ore  body  is  usually  found  by  driving  ahead  through  the 
dike,  on  the  same  dip  as  the  vein  above.  On  the  other  hand, 
veins  frequently  cut  hard  dikes,  and  many  miners  dwell  upon 
such  a  fact,  when  it  occurs  in  their  properties,  but  the  fact  that 
a  vein  cuts  a  dike  only  proves  continuity  of  vein,  which  is 
important,  but  veins  that  cut  dikes  are  younger  than  the  dikes, 
and  the  lack  of  age  in  a  vein  is  a  strong  indication  of  imper- 
fect mineralization,  so  that  a  vein  or  ore  body  that  is  itself  cut 
or  faulted  by  dikes  is  much  to  be  preferred. 

The  term  Fault  is  frequently  used  to  denote  a  fracture 
or  fissure  in  rock  formation,  but  strictly  speaking  a  Fault  in  a 
vein  ore  body  expresses  the  amount  of  the  displacement  of 
the  rock  strata,  and  has  no  reference  to  the  crack  or  fissure 
which  preceded  the  fault  itself. 

67.  The  Fault  Plane  is  the  line  of  fracture  along  which 
the  slipping  occurs.  A  fault  line  or  fracture  has  strike,  dip, 
hanging:wall  and  foot-wall,  like  fissure  veins,  and  the  defini- 


236     PRACTICAL  GEOLOGY  AND  MINERALOGY 

tions  given  for  strike,  dip,  etc.,  will  apply  to  fault  planes 
equally  well. 

With  respect  to  origin,  there  are  several  kinds  of  Faults, 
but  nearly  all  the  faults  that  occur  in  metal  mining  belong  to 
the  class  known  as  Slipped  Faults.  With  respect  to  the 
direction  of  wall  movements  along  a  fault  plane,  faults  are 
classed  as : 

( 1 )   Normal  Faults,  and 

(2) Reversed  Faults. 

68.  A  Normal  Fault  is  the  effect  of  slipping  of  the 
hanging  wall  downward,  or  a  movement  of  the  foot-wall 
upward,  or  both  these  movements  combined.  Nine  out  of  ten 
faults  are  Normal.  A  Reversed  Fault  is  formed  by  a  move- 
ment in  a  reverse  direction  from  a  Normal  Fault ;  that  is,  an 
upward  movement  of  the  hanging  wall  or  slipping  down  of 
the  foot-wall. 

Fig.  70  illustrates  a  Normal  Fault.  The  diagonal  line 
A-D  is  the  Fault  Plane.  The  strata  at  the  right  and  above 
the  strike  plane,  forming  the  hanging  wall,  has  either  slipped 
downward  or  the  foot-wall  has  been  pushed  upward.  The 
fault  or  amount  of  displacement  is  represented  by  the  line 
B-C.  The  horizontal  displacement  represented  by  G-C  is 
called  the  Heave,  and  the  vertical  dislocation,  B-G,  is 
called  the  Throw. 

Suppose  an  incline  shaft  at  F  continued  along  the  dip  of 
the  vein  to  point  C,  where  it  was  found  to  stop  abruptly. 
The  presence  of  "stria"  (marks)  of  slickensides  on  the  walls 
of  the  fault  plane  would  confirm  the  supposition  of  a  faulted 
vein  and  ore  body.  The  question  then  to  determine  is, 
whether  it  is  a  Normal  or  Reversed  Fault.  Inasmuch  as 
Normal  Faults  are  common  and  Reversed  Faults  unusual,  the 
presumption  would  be  strong  that  the  hanging  wall,  or  the 


MINERAL  DEPOSITS 


237 


portion  above  the  fault  plane  A-B,  has  slipped  down  towards 
the  point  D.  The  wall  markings  will  often  indicate  the 
direction  taken  by  the  faulted  ore  body,  or  a  small  seam  of  ore, 
sheared  off,  will  often  be  found  on  the  side  of  the  lost  ore 
body.  If  these  physical  evidences  are  not  decisive,  a  simple 
rule  that  can  be  easily  applied  is  as  follows  : 


Fig.  70.      Ideal  Section  Illustrating  Faulted  Ore  Bodies. 

FAULT  RULE. 

69.  The  continuation  of  a  faulted  ore  body  is  always 
found  on  the  side  of  the  larger  angle  formed  by  the  inter- 
section of  the  vein  with  the  fault  plane. 

A  measurement  of  the  angles  may  be  made  by  any  miner, 
with  an  ordinary  carpenter's  square,  which  forms  a  perfect 
right  angle,  and  the  direction  of  the  displaced  ore  body  easily 
determined. 


238     PRACTICAL  GEOLOGY  AND  MINERALOGY 

In  Fig.  70  the  angle  formed  at  C  by  the  intersection  of 
the  hanging  wall  of  the  vein  F  with  the  hanging  wall  of  the 
fault  plane  A-B  will  be  greater  than  a  right  angle,  and  the 
lower  angle  at  C,  formed  by  the  junction  of  the  foot- wall  of 
vein  with  the  fault  plane,  is  plainly  less  than  a  right  angle, 
which  establishes  the  fact  that  the  displaced  ore  body  is  above, 
the  faulted  vein  appearing  at  B-E,  The  proper  method  is  to 
drive  upward  along  the  fault  plane  to  reach  the  point  B.  If 
on  the  other  hand  the  larger  angle  occurs  on  the  opposite  side, 
it  would  prove  a  reversed  fault,  and  the  missing  ore  body 
would  be  found  by  driving  along  the  fault  plane  towards  D. 
By  following  this  simple  rule  the  direction  only  will  be 
indicated,  and  the  question  of  the  amount  of  displacement  in 
feet  is  still  left  for  determination.  There  are  rules  for  com- 
puting the  distance  between  the  two  sections  of  a  displaced 
ore  body,  but  they  are  outside  the  scope  of  this  book,  however, 
it  is  often  possible  to  measure  a  fault  on  the  surface.  A  fault 
crossing  a  mountain  will  often  show  by  a  depression  or  "sad- 
dle." Sometimes  the  line  of  a  fault  can  be  traced  on  the 
surface  by  the  outcropping  of  rock,  whose  strike  and  dip  are 
different  from  the  surrounding  strata.  The  slip  or  fault  may 
sometimes  be  actually  measured  on  the  side  of  a  cliff  or  canyon 
by  taking  well  defined  strata  above  and  below  and  measuring 
the  distance  between  them,  which  distance  will  be  approxi- 
mately the  amount  of  displacement  of  the  ore  body  within  the 
mine. 

These  simple  methods  are  practical  when  the  displace- 
ment is  no  more  than  a  few  hundred  feet,  but  when  a  fault 
runs  into  the  thousands  of  feet  only  an  accurate  knowledge 
of  the  geological  features  of  the  entire  district  will  be  of  any 
value.  However,  such  surface  examination  will  often  reveal 
a  fault  of  such  extent  that  would  make  it  impractical  to  drive 


MINERAL  DEPOSITS 


239 


along  the   fault   plane   the   required   distance   to   reach   the 
faulted  ore  body. 

Fig.  No.  71  shows  a  series  of  faults  in  a  Colorado  mine. 
Note  the  shaded  section  showing  the  ore  body  faulted  in  its 
downward  course  in  two  places.  The  "Smuggler"  fault  is 
only  a  slight  displacement,  but  the  "Delia"  fault  is  greater. 

Fig.  71. 


Sranire 
VEINS  AND  FAULTS  AT  ASPEN. 

The  greater  angles  are  readily  distinguished  with  the  eye, 
situated  to  the  left,  in  the  direction  of  the  displaced  ore. 
These  faults  are  horizontal  and  nearly  parallel  with  the 
surface,  and  are  sometimes  called  "Shoved  Faults" ;  one 
section  of  the  vein  being  torn  off  and  shoved  away  by  lateral 
pressure. 

By  referring  to  Fig.  64,  ilustrating  Contact  Veins,  it  will 
be  seen  that  Vein  E  is  faulted  normally  by  contact  fissure 
vein  D ;  the  "younger  strata*'  representing  the  hanging  wall 
of  vein  D  has  slipped  downward  as  indicated  by  the  arrow  at 


240     PRACTICAL  GEOLOGY  AND  MINERALOGY 

A.  The  "Blind  Fissure,"  G,  is  a  reversed  fault.  The 
hanging  wall  of  vein  C,  which  is  also  the  hanging  wall  of 
fault  plane  G-C,  has  either  moved  upward  or  the  slate  foot- 
wall  has  slipped  downward. 

Note  that  the  larger  angle  is  at  the  lower  side  at  G, 
showing  the  direction  of  the  faulted  vein,  indicated  by  the 
arrow  and  seen  in  the  slate  below. 

Concluding  Observations 

The  problem  of  faulted  ore  body  often  results  in  aban- 
donment of  a  mine  or  prospect  by  those  unfamiliar  with  the 
subject,  or  the  matter  is  submitted  to  a  Mining  Engineer  for 
solution,  inasmuch  as  it  involves  a  knowledge  of  Geology  and 
higher  mathematics,  but  if  the  principles  named  above  are 
thoroughly  mastered,  the  solution  of  the  simple  faulting 
problems  that  arise  in  the  development  of  a  prospect  or  mine 
will  be  rendered  comparatively  easy  to  any  one  with  common 
school  education  and  good  judgment. 


INDEX 


Acid  Mineral  Tests      124 

Acid    Minerals;    what    are    they 

104 

Actinolite    102 
Ages;    Geologic     26 
Age;   Geologic    42 
Age  of  the  Earth     43 
Age;   Silurian     50 
Albite     102 
Alkali   Minerals;    what   are 

known  as     104 
Altaite    100 

Aluminum   (Element)     96 
Aluminum   Minerals    147 
Alunogen     99 
Amygdaloid     74 
Amphibole    154 
Ancient   River    Deposits     191 
Ancient    River   Deposits;    origin 

of    193 

Andesite     160 
Anglesite    99-134 
Animal   Kingdom     31 
Anthracite     158 
Antimonides     100 
Antimony    (Element)     96 
Apatite     103-150 
Aqueous  Rocks     73 
Aragonite     149 
Argentite    128-99 
Arsenic    (Element)     96 
Arsenide  Minerals     99 
Arsenolite     98 
Artesian  Wells     27 
Asbolite    137 
Ascending    Waters    179 


Ascending    Waters;     theory    of 

183 

Asphaltum    157 
Atacamite    101-133 
Azoic  Era;   what  constitutes? 

47 
Azurite     132-102 

B 

Banded  Veins;   theory  of  origin 

214-215 

Barite    99-151 
Barium   (Element)     96 
Barium  Minerals    151 
Basalt     56-76 
Bauxite    148 
Beach  Deposits;  what  are  they? 

191 
Beach   Placers;    how   formed? 

193 

Bedded  Deposits    190 
Bed  Deposits;  what  are  they? 

190 

Bismite     98 

Bismuth   (Element)     96 
Bismuth   Minerals     142 
Bismuthinite     99-143 
Bismutite    102 
Blanket   Fissure   Vein    214 
Boracite    103 
Borates     103 
Bornite    131 
Boron   (Element)     96 
Boulders;   Glacial    41-42 
Breithauptite    100 
Bromides    97-101 
Bromine    (Element)     96 
Bromyrite     101-130 


246 


INDEX 


Cadmium    (Element)     96 

Calamine    102 

Calamite     135 

Calavarite     127 

Calcareous  Rocks     66 

Calcareous  Rocks;   origin  of    67 

Calcite     67-102-149 

Calcium   (Element)     96 

Calcium  Minerals     149 

Calomel     101 

Carbon     51-96 

Carbon  Minerals     155 

Carbonate     97-102 

Carboniferous  Age;   what  is 
known  of?    51 

Carnotite     142 

Cassiterite    98-124-139 

Celestite    99 

Cenozoic  Age     54 

Cerargyrite     101-123-129 

Cerrusite     102-123-133 

Chalcocite     99-123-131 

Chalcopyrite     123-131 

Chalk   Period     54-67 

Chalk  Strata    45 

Chamber    Deposits;    what    are 
they?     223 

Chemical  Agencies    174 

Chemical  Properties  of  Minerals 
125 

Chlorides     97-101 

Chlorine    (Element)     96 

Chlorite-schist     78 

Chromium    (Element)     96 

Chrysoberyl    149 

Chrysotile     154 

Cinnabar    99-123-138 

Classification     of     Mineral    De- 
posits   189 

Cleavage    113 

Coal  Beds     52 

Coal    Measures;     how    formed- 
196 

Cobalt    (Element)     96 

Cobalt   Minerals     136-7 

Cobaltite     110-137 


Colmanite     103 

Color  of  Minerals     107 

Coloradoite     100-138 

Compounds;  what  are  they?     93 

Concentrating   Agencies     173 

Conglomerate     73 

Contact    Veins; what    are    they? 
217 

Contemporaneous    Formation 
179 

Contemporaneous     Formation; 
theory  of     179 

Copper    96-130 

Copper  Minerals     130 

Corundrum    98-148 

Country   Rock    (definition)     203 

Country  Rock   Rules     232 

Cretacious    Period ;    peculiarity 
of    54 

Crust    Changes;    due    to    Action 
of  Air  and  Water     36-7 

Crust;     Elevation    and    Depres- 
sion    27 

Crust     of     Earth;     evidence     of 
Glacial  Action  on     40 

Crust  of  Earth;   how  is  History 
divided?     46 

Crust  of  Earth;  is  it  stable?     32 

Crust  of  Earth;   three   zones  of 
57-185 

Cryolite     101-147 

Crysocolla     102-132 

Crystal  Form     114 

Crystals;   Hexagonal     117 

Crystals;   Isometric     116 

Crystals;    Monoclinic     119 

Crystals;    Orthorombic     116 

Crystals;    Tetragonal    116 

Crystals;   Triclinic     119 

Crystals;   what  causes  the   end- 
less variety  of    120 

Crystalline  Structure     113 

Crystallography    116 

Cuprite     98-110-130 


INDEX 


247 


Deposits;    Chambers     222 
Deposits;  Mineral  (how  formed) 

173 

Descending  Waters     179 
Descending    Waters;    theory    of 

181 

Descloizite     104 
Devonian  Rocks;   how  to  tell 

them     50 
Diamond     155-6 
Diatoms     71 
Dikes     201 
Dikes;  origin  of     86 
Dikes;  what  are  they    85 
Diorite     74 
Dip    203-4 
Displacement     235-6 
Dolomite     68-150 
Domeykite     99-110 
Dyscrasite     100 


Earth;  form  of    22 

Earth;    is    the   interior    hot?     26 

Earth;   origin  of     25 

Earth;    temperature   increases 
with  depth     27 

Earth;   structure  of     23 

Earth;  age  of    42-3 

Earth;  what  is  it?       22 

Earth;  what  materials  make 
up?     168 

Earth's  Crust;  evidence  of  Gla- 
cial Action     40 

Earth's    Crust;    Elevation   and 
Depression     27 

Earth's    Crust;    how    is    History 
divided?     46 

Earth's  Crust;  is  it  stable?"  32 

Earth's    Crust;    three    zones    of 
58 

Earth's    History;    how    do    Fos- 
sils record?    44 
Earth's  Movement     33 
Earthquakes     28 
Elaterite    156 


Electric  Currents     179 
Electric   Currents;    theory   of 

180 

Elements     168 

Elements;    how   classified?    96 
Elements;  what  are  they?     93 
Embolite     101-130 
Endings;  what  do  they  signify? 

97 

Epsomite     99 
Evaporation     175 


Fahlbands;  what  are  they?     226 

Faults     201 

Faults;  how  they  affect  ore 
bodies  234 

Faults;   what   are   they?     83 

Fault ;   normal    236 

Fault;   plane     236 

Fault;    reversed     236 

Fault;   rule     237 

Fault ;   slipped     236 

Feldspar     72-108 

Fissure  Vein  Blanket     214 

Fissure  Veins;  how  may  age  be 
determined?  87-216 

Fissure   Vein;    true     212-13 

Fissure  Veins;  what  are  they? 
212 

Flowage  Zone;  what  is  known 
about  it?  59-187 

Fluorides     101-97 

Fluorine    (Element)     96 

Fluorite     101-160 

Folds;  what  are  they?     83 

Formulas;  what  are  they?     94 

Fossils;   Fresh  Water     45 

Fossils;  Salt  Water     45 

Foot  Wall    203 

Fracture     112 

Fracture  Zone;  what  distin- 
guishes? 58-9 

Franklinite     136 

Friction     28 

Fusibility  Scale     122 

Fusion     175 


248 


INDEX 


G 

Galena     99-134 

Gangue     202-213 

Gangue    Minerals;    what    are 

they?     159-60 
Garnet     159 
Garnierite     102-137 
Gash  Veins     219-20 
Geologic   Ages     46 
Geologic   Age;    practical   mining 

lessons  of     57 
Geologic  Age;   what  are  known 

of    42 

Geologic   Survey  Maps   and   Re- 
ports;  how  to  use     61-2 
Geology;  what  is  it?     21 
Geology;    why    a    knowledge    is 

necessary    21 
Gerhardite     103 
Geysers     27 
Glacial  Action  on  Earth's  Crust 

40 

Glacial  Boulders     41 
Glacial   Drift;   causes  of    41 
Glaciers  in   Greenland     40 
Glaciers;   was  the  Pacific  Coast 

affected  by    42 
Glaciers;    what   are   they?  what 

changes  do  they  produce?     39 
Gneiss     78 

Gold  Minerals     126-7 
Gold   (L.  Aurum)   Element     96 
Gold    Telluride   Minerals     127 
Granite;    definition    of;    how 

formed     77 

Granite;  primary  rocks     43 
Granular   Quartz     70 
Graphite     156 
Gravity    37-172 
Greenland;    Glaciers   of    40 
Gypsum    99-150 
Gypsum;   what  is  it?    68 

H 

Halite     101-151 
Hanging  Wall    203 
Hardness     108 

Hardness;    Practical   Field   Test 
for    109 


Hardness;    scale   of    108 
Hardness;   table   of    109 
Hematite;     98-144 
Hessite     100-129 
Hexagonal   Crystals    117 
High    Grade     200-213 
History  of   Earth;    how  do   fos- 
sils record?     44 
Hornblends     72-159 
Horses     204 
Horsfordite    100 
Hot   Springs     27 
Hubnerite     103-140 
Hydrocarbon    Minerals     156 
Hydrogen    (Element)     96 

I 

Igneous  Injection     179 
Igneous    Injection;    theory    of 

180 

Igneous  Rocks     43-57-73 
Igneous  Theory    171 
Impregnation  Deposits;  what 

are   they?    224 
Iodides     97-101 
Iodine    (Element)     96 
lodyrite     101-130 
Irregular  Deposits     189-22 
Iridium    (Element)     96 
Irodosmine    144 
Iron  (L.  Ferrum)  Element     96 
Iron  Minerals     144-5 
Isometric    Crystals     116 


Jamesonite     134 

Jurrassic    (Division  of  Mesozoic 
Era)     53 


Kaolinite     102 
Kingdoms;  three     30 
Kingdom;  Animal     30 
Kingdom;   Mineral     31 
Kingdom;   Vegetable     30 
Knowledge;    Mental    and    Moral 

16 
Krennerite     128-100 


INDEX 


249 


Lateral  Secretion     179 
Lateral   Secretion;    theory   of 

188 

Lava     76 
Lead     (L.     Plumbum)     Element 

96 

Lead    Minerals     133 
Lignite     54-157 
Lime     98 
Limestone     68 
Limestone    Strata    45 
Limonite    145 
Liquids     25 
Lode     202 
Luster    106 

M 

Manganese     (Element)     96 

Manganese   Minerals    146 

Manganosite     98 

Magnetite     145 

Magnesite     153 

Magnesium     96 

Magnesium  Minerals     153 

Malachite     132 

Mammals;  age  of    54 

Maps;    Geological    Survey     61 

Marble;   composition  of     68 

Marcasite     99 

Marshite     101 

Materials;   in  the  Earth     23 

Mechanical    Agencies     174 

Mercury     (Hydrargyrum)     Ele- 
ment    96 

Mercury    Minerals     138 

Melaconite     123-131 

Melonite     100 

Metamorphic  Rocks     76 

Meteors     29 

Meteoritic    Theory;    what   is   it? 
29 

Mesozoic   Era;    what   character- 
izes?   52 

Mica     72 

Mica  Schist     78 

Millerite     99-138 

Milky  Quartz     70 


Mimetite     134 
Mineral  Belt     203 
Mineral  Coal     157 
Mineral   Deposits     167 
Mineral  Deposits;  how  classi- 
fied?   188 
Mineral   Deposits;    how   formed? 

173 
Mineral  Deposits;   Nature's 

preparation    for    188 
Mineral  Deposits;  origin  of    169 
Mineral    Deposits;     Relation    to 

Mountains     36 
Mineral  Kingdom     31 
Mineralogy;     definition     92 
Mineral  Tests     121 
Mineral;   what  is   it?     91 
Minerals;   Acid;  what  are  they? 

104 
Minerals;    Alkali;    what    are 

known  of    104 
Minerals;    Antimonides    100 
Minerals;   Arsenide    99 
Minerals ;    Borates     103 
Minerals;   Bromides     101 
Minerals;   Carbonates     101 
Minerals;     Chemical     properties 

of    125 

Minerals;     Chlorides     100-101 
Minerals;   Fluorides     101 
Minerals;    Gangue     159 
Minerals;   how  formed     91 
Minerals;   how  grouped     97 
Minerals;    how  to   examine   and 

determine     125-6 


Minerals; 
Minerals; 
Minerals ; 
Minerals; 
Minerals; 

of  105 
Minerals; 
Minerals; 
Minerals; 
Minerals; 

123 
Minerals; 


Iodides    101 
Molybdates     104 
Nitrates    102 
Phosphate     103 
Physical   Properties 

Silicates    102 
Sulphate     99 
Sulphide     99 
Table    of    Fusibility 

Tellurides    100 


250 


INDEX 


Minerals;    Tungstate     103 

Minerals;  Vandates     104 

Mining;  mistakes  due  to  ignor- 
ance and  inexperience  227-8 

Minium     98 

Miscellaneous  Ore  Rules     233 

Mistakes  due  to  experience 
with  bad  judgment  229 

Molten  Zone;  what  is  known 
about  it?  60 

Molybdates     104 

Molybdenite     99 

Molybdenum    (Element)     96 

Molybdenum   Minerals     142 

Monoclinic    Crystals     119 

Mother  Lode     53-203 

Mountains;  what  proof  exists 
that  they  have  been  uplifted 
35 

Movement;   Earth's,    the     33 

Muscovite     153 

N 

Nagyagite     86-127-100 

Natron     102 

Natural  Laws;  what  are  they? 
17 

Nature's  Preparation  for  Min- 
eral Deposits  188 

Nebulae     29 

Nebular   Hypothesis     29 

Niccolite        99-138 

Nickel    (Element)     96 

Nickel  Minerals     137 

Niter     103-152 

Nitrates     102-105 

Nitratine     152 

Nitrobarite    103 

Nitrogen    (Element)     96 

Normal  Fault     236 

North    American    Limestone 
Strata     45 

Northern  Drift     40 

Nuggets  in  Placers    194 


o 

Obsidian     76 

Olivenite     133 

Open  Fissure     202 

Ore   Bodies;    how  do  Faults  af- 
fect?    234 

Ore  Chimney     206 

Ore     Deposits;     common     errors 
regarding     227 

Ore  Deposits;  general  principles 
governing    231 

Ore    Deposits;    ideal    section    il- 
lustrating origin  of    185-6 

Ore  Deposits;  irregular     223 

Ore    Deposits;    what    physical 
conditions     influence?     201 

Ore  Shoot  Rules     232 

Ore     Shoots;     what    are    they? 
206 

Ore;   what   constitutes?     198-9 

Origin  of  Calcareous  Rock     67 

Origin  of  the  Earth     25-6 

Orthoclase     137-102-153 

Orthorhombic    Crystals     118 

Osmium    (Element)     96 

Outcrop     204 

Oxides    98 

Oxide    Zone;     what     character- 
izes?    58-9 

Oxygen   (Element)     96 


Pacific    Coast   Affected   by   Gla- 
ciers   42 

Paleozoic   Era;    what   marks? 
46-49 

Palladium    (Element)     96 

Patronite     99 

Pay- Streak    213 

Periclase     98 

Petroleum     157 

Petroleum;    how  formed?     196 

Petroleum;  what  is  it?    196 

Petrology;  what  is  it?     65 

Petzite    127 

Phosphates    103-97 

Phosphorus    (Element)     96 


INDEX 


251 


Physical  Properties;  how  to 
make  practical  application  of 
160 

Physical  Properties  of  Minerals 
105 

Pink  Quartz     70 

Pipes  of  Ore     206 

Placer  Deposits;  what  are  they? 
191 

Placers;  origin  of  nuggets  in 
194 

Platinum   (Element)     96 

Platinum  Minerals    143 

Polybasite    129 

Porphyry    74 

Potassium   Minerals     152 

Potassium  (Kalium)  (Element) 
96 

Powelite    104 

Practical  Application  of  Physi- 
cal Properties  160 

Practical  Field  Method  for  Spe- 
cific Gravity  112 

Practical  Field  Test  for  Hard- 
ness 109 

Practical  Use  of  Theories     30 

Precipitation     177 

Proustite     129 

Pseudomorphs ;  what  are  they? 
120 

Pumice     76 

Pyrargyrite    129 

Pyrite     146 

Pyrolusite     146 

Pyromorphite    134-103 

Pyroxine     159 

Pyrrhotite     146 


Quarternary  Period;  changes  of 

56 

Quartz     70-98-158 
Quartz;  origin  of     70 

R 

Radiant  Energy  of  the  Sun    37 
Realgar    99 

Relative     Proportions     of     Ele- 
ments   167-8 


Replacement     179 
Replacement;    theory  of    ,183 
Reports;    Geological    Survey 

61-2 

Reversed   Faults     236 
Rhodocrosite     132-102-147 
Rhyolites     56 
Rocks;   Aqueous     72 
Rocks;   Calcareous     66 
Rocks;  how  classified     72 
Rocks;  Igneous     72 
Rocks;  Metamorphic     76 
Rocks;   of  what  composed     6? 
Rocks;   Stratified     79 
Rocks;   Trap    74 
Rocks;  Unstratified    79-84 
Rocks;  Volcanic    75 
Rock;  what  is  it?    65 
Rules;   Country  Rock     232 
Rules;  Fault    237 
Rules;    Miscellaneous     233 
Rules;   Ore  Shoot     232 
Rules;  Vein     231 
Rutile     98-140 


Sandstone    73 

Sal   Ammoniac    101 

Scale  of  Fusibility    123 

Scale  of  Hardness     108 

Scheelite     125-103-140 

Science;  what  is  it?    16 

Sea  Water  Theory    170 

Sedimentary  Rocks     81 

Segregation   Veins     220 

Selenium   (Element)     96 

Sellaite    101 

Serpentine    154 

Shale     73 

Shoots;     ore;     what    are    they? 

206 

Shoved  Fault     239 
Siderite     102-130 
Silica  Minerals     158 
Silicate  Minerals    159 
Silicates     97-102 
Silicates;    what   are   they?    71 
Silicious  Stones;  what  are  they? 

69 


252 


INDEX 


Silicon    (Element)     96 

Silurian  Age;  what  distinguish- 
es it?    50 

Silver    Minerals    128-9 

Silver    (Argentum)    Element    96 

Slate     73 

Slipped  Faults    236 

Smaltite     122-99-137 

Smithsonite     102-135 

Smoky  Quartz     70 

Soda  Niter    103 

Solids     25 

Sodium  Minerals    151 

Sodium    (Natrum)    Element     96 

Solution     177 

Specific  Gravity    111 

Specific   Gravity;   practical   field 
method  for    112 

Sperrylite     144-99 

Sphalerite     135-99 

Stannite    139 

Stephenite     129 

Stibnite     100 

Stockwork    Deposits;    what    are 
they?     224 

Stolzite     104 

Strata  Chalk     45 

Strata    Chalk;     formation     and 
groups     45 

Strata;  limestone    45 

Stratified    Deposits;     what    are 
they?     190 

Stream  Deposits    191 

Stream  Placers     191 

Stria     39 

Strike    203 

Stromeyerite     128 

Strontianite     102 

Strontium    (Element)     96 

Structure;    Crystalline     115 

Structure;  Earth's     23 

Sublimation     174-176 

Sublimation;  theory  of    182 

Subterraneum  Theory    171 

Sulphate  Minerals    99 

Sulphide   Minerals    97-99 

Sulphide   Zone;    what   distin- 
guishes?   59-185 


Sulphur   (Element)     96 

Sun;  radiant  energy  of    37 

Syenite     78 

Sylvanite     100-127 

Sylvite    86-152-101 

Symbols;  what  are  they?    94 


Table  of  Fusibility  of  Minerals 

123-4 
Table   of   Hardness  of   Common 

Minerals     109-10 
Talc     139-102-155 
Talcose  Schist     78 
Tantalum  (Element)     96 
Tellurides     100-97 
Tellurite    98 

Tellurium    (Element)     96 
Tenacity     113 
Tertiary  Period     55 
Tests  for  Acid  Minerals     124 
Tetradamite     100-143 
Tetragonal    Crystals     116 
Tetrahedrite     132 
Theories;  what  conclusions  may 

be  drawn  from     184 
Theories;  what  practical  use 

are  they?    30 
Theory   of   Ascending   Waters 

183 
Theory     of    Contemporaneous 

Formation     179 
Theory    of    Descending    Waters 

181 

Theory  of  Electric  Current    180 
Theory    of     Igneous     Injections 

180 
Theory     of     Lateral     Secretion 

182 

Theory  of  Replacement    183 
Theory   of   Sublimation     182 
Titanium   (Element)     96 
Tin     (L.     Stannum)     (Element) 

96 

Tin  Minerals     139 
Titanite     141 


INDEX 


253 


Titanium   Minerals    140 

Trachite     75 

Trap  Rocks    74 

Triclinic  Crystals    119 

Triassic    (Division    of    Mesozoic 

Era     52 

Tungstates    103 
Tungsten    Minerals     139-40 
Tungsten   (Wolfram)    (Element) 

96 

Tungstite     98 
Tourmaline    159 
Turquoise     149 

U 

Unstratified   Deposits    198 
Unstratified    Rocks     84 
Uraninite    142 
Uranium    (Element)     96 
Uranium  Minerals    141 

V 

Valentinite     98 
Vanadates     97-104 
Vanadinite    104 
Vanadium  Minerals     141 
Vaporization     174 
Vegetable   Kingdom     31 
Vein  Rules     231 


Veins  Banded;  theory  of  origin 

of     214-15 
Veins;  do  they  grow  richer  with 

depth?     209 
Veins;    gash;    what    are    they? 

219 

Veins;   origin  of    86 
Veins;     Segregation;    what    are 

they?    220 

Veins;  what  are  they?    87-202 
Veins;   true  Fssure     213 
Volcanic  Rocks     75 
Volcanoes     28 

w 

Wall  Rocks     201 

Water    98 

Western   Europe;    Chalk    Strata 

45 

Willemite    136 
Witherite     102-151 
Wolframite     103-139 
Wulfenite     127-104-142 


Zincite     121-98-136 
Zinc  Minerals    134 
Zones;  Molten     60-187 
Zones;  Oxide     60-185 
Zones;    Sulphide     169-60-185 


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